Although I don't mean to speak for Rocksuitcase, pretty sure he means the ability to use the raw files that were recorded to one phone on another without requiring conversion. The method of transfer between the phones is irrelevant.
2. as far as feeding other mics into a d:vice, if its anything that needs a special power supply like schoeps etc its kind of overkill (and expensive), vs a cheaper, smaller, more battery efficient, more reliable A10. the sax obviously has phantom and 5V PIP and thus can power basically anything with the right mic bodies (real phantom). but any of the active boxes like nbox/tinybox etc, d:vice cant do that (elegantly)
That's very much an apples and oranges comparison, and incorrect or irrelevant in a number of ways.
First we should clarify what is meant by "active". The only boxes that quality as being "active" in the way that term is used by Schoeps and around TS, are those which supply high-voltage to externally polarized microphone capsules, eliminating the microphone amplifier bodies. Those include: nbox, baby nbox and tinybox (depending on configuration), maybe some other Naiant devices, and certain Schoeps preamps that I'm only vaguely familiar with and aren't really relevant here. All of these are "active" solutions which do not require any power being supplied from the recorder. (FYI- depending on configuration, Naiant PFA can also be an "active" solution which eliminates the microphone amplifier bodies, yet requires phantom power from the recorder, making it irrelevant to this discussion)
The others, including MMA-A, are not "active" in the same sense, as they are incapable of powering externally polarized capsules, including Schoeps.
MMA-A is not "overkill" for Schoeps mics, it is a "no kill" - it will not work at all because it is unable to power them. MMA-A can, however, provide a very similar solution to "active" boxes for tapers using standard interchangeable DPA capsules. This is because all DPA capsules are pre-polarized and do not require any external polarization supply. This requires a special DPA amplifier/cable that looks similar to, and essentially serves a similar practical role as an "active cable".
^
That's not the typical use of MMA-A though. Most folks will be using DPA miniature microphones connected directly to the MMA-A.
The M2D2 is an entirely different animal. Its a full featured external preamp/ADC, for use with complete microphones. It is not "active" in that it is unable to provide polarizing voltage directly to capsules. Yes, you could plug a pair of PFAs configured to power an "active" microphone setup in to it, but that's not relevant to this discussion.