I've worked with my Walther P99C enough that I'm comfortable carrying it. I ended up with four full-size magazines w/sleeves and three compact ones, two with the pinky extension and one with the flat base pad. I'll carry it loaded with a compact mag w/pinky extension in the gun and a full-size mag w/sleeve as a spare.
I've found that there's no discernable difference in my shooting with the FS mags and the ones with the pinky extension, but the one with the flat bottom slows me down. At this point, the flat-bottomed one is relegated to LAMR status. I've read that some folks like the flat-bottom mags for pocket carry, but the Walther's too big for that.
Am I missing something, or is the flat-bottomed mag really at a tits-on-a-boar level of usefulness?