Just for my info only...I own a P99c and really like it but I don't see a reason to buy extra mags for it when my full size mag fit it...is you desire to purchase extra mags simply a matter of what you want? Just curious?
I always get 5-6 mags per pistol. Just old habit I guess. I don't like having only 2 mags. Some day, it may be hard/expensive/impossible to get the mags, so whenever I purchase an auto pistol, new or used, I always order plenty of mags for it.
And yes, the full-size P99 mags work great in the compact, but like someone else said, the size and feel is much different.
Some people claim it is easier to conceal - I personally would rather have the finger grip on it - When I first got mine, I couldn't shoot too well w/ the mag w/ the flat floor plate. After 2 mags of that, I picked it up and just kept reusing that 1 mag.
Someone on the AR15 website was nice enough to mail me a floor plate for free, so I now have that on both of my mags. And, if I wish, I can use my full size mags in my compact and have 16 rounds.
Primarily concealment reasons to go with the flat bottom magazines, at least for me.
My P99c AS resides primarily in the front pocket of my vehicle's driver seat (neat thing that Saab does in its vehicles, although I'm sure the Swedes never thought it'd be used for this purpose), and with the finger rest in the pistol it protrudes every so slightly above the lip of the pocket - the flat bottom mag allows the lip of the pocket to close over it and be invisible, even when the car is cleaned (while me watching closely of course) or being serviced.
This morning CDNN said they only had one kind in stock and thought it was without the finger rest. I bought one to try it. If it doesn't do if for me I can order another when the finger rest model is back in stock (or look for the floor plate only.)