the mod t states it can use 3rd party filaments.

Can't see any issues. And the term 'pla' now applies to hundreds of different materials all with different manufacturing processes and formulas.
There is a pla filament out there with pretty much any characteristic you need. Abs - not so much :-)
Flexible pla (I know of at least three companies making this) tends to be much easier to print than ninjaflex or the other rubber based flexi-filaments.

Your best bet is to get some samples from globalfsd - they have a us branch now as well - and just try it out before committing lots of money to full rolls.
http://www.globalfsdusa.com/?target=main