Hey @The Documentary Sound Guy, a reasonable query.
My query in this case is in relation to the M2D2's place in the workflow of a radio journalist, where its proves handy on reporting trips, first in field and later in the edit and tracking. While certainly a question of technique and approach, in the field a devices small profile can assist in easing the casual nature of the moment as the source/interviewee speaks with the reporter, it's small size being a unique advantage over mixer/recorders like the Nagra 7/Mixpre/ etc. Though like both those units, when returning after a day in the field, the M2D2 has the benefit of doubling as the audio interface during the edit, tracking, and playback.
As for what a field reporter might couple the M2D2 with. While using your phone in the field make sense in theory (Sonosax pitched this for journalists), there are times you are recording both ends of a sudden phone call (using both of the M2D2's inputs, recording into....?) or when you need your phone handy for incoming messages (say during a satellite two-way). That said, totally, a spare phone just for the M2D2 is an option, though seems like there'd be a simpler option? Which brings me back to Lectro's SPDR, which seems most fitting in this context (albeit pricier than a spare phone). Which is why I wondered wonder if there were any comparable alternative low profile recorders to pair with the M2D2 that maybe centered around USB or AES (such as TE's TP-7, although designed for a very different audience).
But hey maybe an extra phone is the convenient option. Good to have a spare.