Mecenas, it is insurance. While 10 rounds should be good enough, you never know. Taking data from police shootings, the hit rate is less than 50%. In some cases as low as 20%. And that is with a full sized service weapon. A subcompact makes it even harder to get hits. What if there are two bad guys? 5 rounds per bad guy, cut that in half (at least). Maybe 2 rounds hit each...on a good day. Now what about the shot placement on those 2 rounds. Yes, 10 should be fine, but you never know.
I keep going back and forth between the RAMI and the P01. P01 has 14 rounds. But is much larger and more difficult to conceal. But I like having the extra rounds. The RAMI is easily concealable and the extra two rounds keep it more concealable than the P01. It does not add much at all. But with the base pad and the grams follower, I get almost the same round count as the P01 in a smaller form.
TNman, it increases round count by 2. Add the grams follower and it could be 13. 10 round mag could get almost the same round count as the 14 round mag but be easier to conceal. Smaller form factor but higher round count.