Seats in row 12 of the A320 are sold as premium seats because as a bulkhead-facing row, they have more leg room that a standard seat offers.

The "gotcha" is that because there is no other seat in front of you, the tray for your meals must fold up and retract into the armrest. To accommodate it, the armrest is a bit wider, and intrudes into the seating area by about three-quarters of an inch or so.

The other "gotcha" with bulkhead seats is that with no seat in front of you, all of your carry-on bags must go into the overhead bin. There is no seat in front of you to stuff a bag under.

I never selected these seats. If you want more legroom, take seats in the exit row. In the A320, you want row 18 (row 17 is also an exit row with additional legroom, but with another exit row directly behind, these seats do not recline). Seats in row 18 have the extra legroom, as well as full recline. As karachi notes, A and F seats in exit rows do not have an outside armrest, due to the proximity of the emergency exit.