I wonder why he can't show an actual picture of one of the TMOUS phones (they have red and green call buttons)?
If assuming that they are genuine TMOUS, and that they are all working fine, then they should be able to flash Nandroid, WP7 and quite a few of the custom ROMs (the chefs should say if their ROM is TMOUS compatible).
The only real major concern is flashing a .51 RADIO - which will turn your nice phone into a rather expansive paperweight. If you are using a stock ROM, then check that it is for a TMOUS.
As for price and value, sorry I don't know enough to comment.