Kel tec 9mm Glock Carbine question

[Vincep]

I know this is a handgun forum but i'm looking for opinions on a kel tec 9mm Glock Carbine. Would i be better off stocking up on 15 or 17 round mags that fit flush in a G 17 or 19 pistol or 31 round extended? Would like to get some opinions. Thanks.

[SCCogswell]

Prices I've seen give a slight edge to the standard capacity G-17 mag ($/round). Dunno about the reliability factor of the extendo-mag; every extended mag I've used in other guns has been *un*reliable, but I've never used Glock extended mags before. Glock certainly has a good reputation for reliability in the 9mm guns (we'll ignore the .40 K-Bs). Since the "social" Sub-2000 will most likely be carried low-profile - folded with a loaded mag inserted - it makes little sense (to me, anyway) to have a mag that sticks out and makes the folded package bigger. You can always hang a couple of 30-rounders in a mag pouch on the forend, sling, stock, etc. Now there's a WECSOG project - inlet each side of the forend to hold a 30-round mag: 77 rounds on the gun!
I'm planning on getting 5 std G-17 mags as the "basic" supply for my Sub-2000, then probably getting a 30-rounder for fun. If it turns out to be reliable, I'll get more. I'm still hoping people start dumping their Clinton mags cheap - I'll stock up on those 10-rounders for range use to reduce wear on the "real" mags.

[Vincep]

Good point. The 31 rounders would detract from the total conceilability of the folded carbine;unless like you said, don't keep the mag inserted in the carbine while folded. 17 rounders aren't bad either. With 2 mags you have 34 rounds. I was wondering if there really was a tactical advantage to use the 31 rounders as opposed to the 15 and 17 flush fit. Any more opinions?