Both of InMath and MathMagic are for creating equations in InDesign documents but their appoaches are completely different

InMath forms an equation by placing characters and symbols in its specific position to make the result look like an equation. So the equation is not saved as a separate image file but rather integrated into the InDesign's text property.

So it is a bit more flexible in changing the font size and style of each component of your equation.

InMath plugin also works with InCopy. If your workflow has some InCopy users for data entry, they can also work with InMath.

InMath can handle most K12 equations but it takes more time if  you have to deal with complex equations or multi-lined equations. So if your equation work should handle lots of equations and comlex equations often including higher Ed level, MathMagic is definitely the way to go.

InMath does not offer any import/export options for other equation formats. So if you have to import any ready made equations, saved in MathType, MathML, LaTeX, out of luck at the moment.

And you may not export the equations as a separate external image unless you make a screen shot. 

Actually it is not an equation editor but more like a special text editor with special styles for Math.

As all the equation handling features are implemented as a plugin, InMath used to have some bugs and compatibility issues when opening InMath equation embeded InDesign documents in a newer version of InDesign.

And InMath only runs witin InDesign so you have to run InDesign to use it. MathMagic and MathType can be used as a standalone application and works with other applications as well.

InMath is quite expensive though(495 Euro) and multi-user discount not available unless 10 or more. And you have to purchase an upgrade whenever Adobe releases a newer version. If youare going to stay tuned with InDesign for many years, you will end up with paying much more. Or, if you have to maintain multiple versions of InDesign(such as CS2, CS3, CS4) for some reasons, for example to work with multiple clients, you will have to purchase each plug-in separately. (Math Magic comes with all plug-ins for InDesign 2.0 or newer if you pay once: US$499.0)

So, if your project is for a short term for a few books, and if you don't mind typing all equations and you don't face any critical deadline, and if more controls over font/size/style/color is important for you, InMath might be the one for you.

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Math Magic has been around for more than 10 years as a standalone equation editor and as a Quark Xtension since Quark 3.x. So you can tell MathMagic is the most advanced full featured equation editing solution for tech writers and designers/publishers once you try it.

It comes with all the bells and whistles, and backed up with productity if you have to handle lots of equations often.

MathMagic Pro eidtion comes two programs: MathMagic application and MathMagic plugin. MathMagc app is the very standalone equation editor application. this app works with other applications and documents via copy-paste or drag-drop just like othr applications. 

MathMagic plug-in is a special addition for InDesign and this adds some UI to InDesign menubar and toolbar and right-button clicked contextual menu, such as "New Equation", "Edit Equation".  Once you select "New Equation", it opens an equation editor window. All the equation writing and editing is done by the external MathMagic Pro application. once done, it places the equation into InDesign doc as an EPS image. You can make it externally saved and linked, or embeded in the doc, from its Preference window. MathMagic pro comes with multiple plug-ins: indesign 2.0, CS, CS2, CS3, CS4, CS5. So you can use MathMagic pro with all versions of Indesign. Althogh Mathmagic company says Math Magic enables you to write equations from within InDesign doc, technically mathmagic plug-in runs its external Mathmagic application. As MathMagic application can read some common math expressions such as MathML, LaTeX, Google Doc equation, Wiki equation, and even MathType equation and some MS Word equations, you will find MathMagic useful if you receive those files. As equations are placed in EPS format in InDesign doc, once you can send the Indesign documents to anyone. They don't have to install MathMagic if they just view or print the document. (Before pringing, they will have to install used fonts to avoid missing fonts as you may understand. But for viewing, EPS preview should work fine without installing fonts unless they do proof reading). So InDesign documents with Mathmagic equations can be shared more easily with others and even across InDesgin versions because EPS is kind of a standard image format all Adobe design products support natively. 

When mathmagic plugin installed, you can simply double click on an equation to re-edit it. this would be the main benifit of MathMagic. Other strengths include automatic baseline alignment when inserted as an inline equation in a text box; you can copy & paste EPS equation within or across your InDesign documents; all equations can be extracted from InDesign document as external EPS files or converted to other formats such as MathML if your clients want. 

Math Magic does not support InCopy.(MathMagic could be installed in InCopy but inserting an equation not worked. We could not figure it out at least. Not sure if they support CS5).

Mathmaigc pro is also expensive ($499) but they have Educational pricing and multiuser discounts and other pricing options. Actually too many options… a bit confusing when you first visit their order page. MathMagic windows version is still not as good as their Mac version. It looks they update their Mac version more often. Their Widnows installer did not work properly so some manual touches were required. 

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MathType can be a reasonable and simple solution if your budget is tight and your client does not care much about the equation quality. 

You can write multiple equations using MathType, save them as EPS file, then place the equations one by one from within your InDesign doc. However, inserting an inline equation manually is a bit inconvenient and the automatic baseline alignment is not supported.

And if you have to reedit an equation, you need a full round trip, which takes more time than MathMagic. But under $100, you get a solution. Or, you can use MathMagic Personal Edition ($69) as MathMagic offers more feature and better equation quality(personal preference) than MathType in general.  MathMagic Personal application does not come with indesign plugin. So just like MathType, you can write your equation and save it as EPS or PDF, then manually place it from Indesign. MathMagic personal edition is a bit cheaper than MathType. MathMagic personal edition comes with most of MathMagic Pro features but color EPS is not supported. So if  you have to use color in your equation, you will have to use MathType or MathMagic Pro. 

If you use MathMagic Pro for InDesign layout, your front-end equation data entry team can use MathMagic Personal edition for a better workflow although Mathmagic Pro can read most MathType EPS files as well. (Mathmagic could not convert some MathType symbols corrctly) 

Sorry for typos if any but hope this helps. 

Please correct me if anything wrong. And we'd like to hear from you guys if you have other solutions or tips.

Not sure if ours were the same problem but we had some issues in saving mathmagic EPS files externally when the InDesign document name or its path had some European characters. This works better now with thier newer updated plugin.

And we've also asked mathmagic company to support both options(saving externally and linking, and embeding) so we can save the equatoin eps externally first and then embed it so that we can have two copies at the same time. They promised to support this last year but no progress until now.

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If your MathType equations are using some type 1 PS fonts, or the EPS files were created on Windows and then brought over to Mac, it looks their EPS printing problem happens more often.

So, you may want to use OpenType or TrueType fonts in MathType equation, if this is an option for you or for your clients.

MathMagic also allows you to use all the fonts installed in your system.

But two things to watch out.

- MathMagic had some issues with some Type 1 PS fonts, especially if you change the style(face) in mathmagic window or if you use some Latin characters. (mathmagic support staff recommended to use OTF or TTF, or convert Type 1 to OTF using a font utility).

- Mathmagic symbols (except Greek) stick to its own Symbol fonts. (this is true with InMath and Mathtype too).

Let me show how I work with MathType in InDesign.
Thanks.