In principle the Maggie and Apogee tweeters are identical. Structurally they are very different. The Maggie tweeter is an individual component which you can remove from the speaker in it's entirety. The Apogee's tweeter magnets are part of the structure of the speaker frame and they can not be removed. Only the tweeter ribbon can be removed which I might add is a very entertaining procedure. I always told people who were considering replacing there own ribbons to buy 4 ribbons at a time. The first two are for practice. The Apogee tweeter is supported along it's length by little foam blocks squeezed in between the magnets at intervals of 12" or so. The Maggie tweeter is supported in it's channel by little blobs of blue something or other between the edge of the ribbon and the channel. The blobs alternate from one side to the other at around 3 inch intervals. IMHO the Maggie tweeter is a better design. It is more durable (but still relatively easy to blow) and much easier to replace. Sonically, I doubt you could tell the difference.
Magnepan Mods
It appears that they are using upgraded crossovers. I guess I'm confused as to why Magnepan wouldn't offer these upgrades themselves. It's super inefficient to pay for shipping both ways, have someone rebuild it, and then wait a few months to get it back...hopefully with no shipping damage. If Magnepan isn't maximizing their products, it seems like a competitor could make a me too product with a better crossover and a nicer stand option. Am I missing something?