I am considering buying MathType since it works well with Scrivener for Mac. However, virtually all my Scrivener writing is done using MultiMarkdown and exported as a MMD txt document.
Does anyone know if MathType will “play well” with MMD and the final export?
Some of the documents I export will be refined in Nisus Writer Pro (ODT export option), many others will be converted to HTML via Marked (TXT export option).
Yeah, it works well. The end product of a MathType object in Scrivener is a normal graphics file, so it works with just about everything except plain-text. If you’ve ever used figures before with MMD then you’ll know what to expect. Scrivener will generate the image syntax for you in the spot where the equation sits, and then export a copy of the file to the compile folder.
Many thanks for your reply. So this might be a problem for me, as my most typical export is as a plain-text multimarkdown file. What happens in that case? All gets lost? Is there an easy way to reconnect an exported image (if any)?
Plain-text, not MultiMarkdown. 
When I said plain-text I meant that literally, as in the compile option. If you write with MMD you probably never use selection choice. Plain-text strips out all graphics and since there is no common syntax for placing them, ignores that they ever existed. MMD on the other hand has the virtue of having syntax for things.
Fantastic. Thanks for the clarification. I was thinking of “plain text files” such as TXT. Got what you mean now. Looks like MathType will be a nice addition for me.