I haven't shot the 250 but i own the 320 and love it. The only difference is hammer vs striker. Since the 250 is hammer fired, the trigger pull is longer and heavier.
Mags and frames and interchangeable with same caliber 250/320. Frames are interchangeable between 9/357/40 but not the 45 since the mags are bigger, and FCU is different.
A lot of people hate the 250 because of the long heavy trigger but i plan on picking one up in 9mm to go with my 320. It'll give me some extra mags and it they seem to be a couple hundred less than the 320 since they aren't as popular.