I didn't get a 2sum, but i wish i did. I just got the p250sc 9mm. You get two different sized pistols in one package. The FCU (firing control unit, or something) has the serial number on it, so you can swap out barrels and grips for different calibers and sizes with the same "gun". I think if you get the 2sum in 40 or 357, you can just buy barrel in the opposite and swap between the two sizes and two calibers in minutes.
The thing people don't like about the p250 is the DAO trigger. I enjoy it and think it is a great gun. If you like the trigger, i highly recommend it. The good thing about the trigger is that you don't need or want a manual safety. The long trigger pull makes it safe to carry without one. I stick one in my pants nearly every day.