I had a G17 version for awhile which is the one I would suggest. Nothing like having a large amount of 17rd and 33rd factory mags available. Its accurate and soft shooting. A cheap Kel-Tec stock extension is nice for those with longer arms. The factory front rail that replaces the plastic insert up front is a nice touch and with both add-ons everything is still compact and keeps it fold-able.
I ended up selling mine because I just didn't have a use for it. I have an AR pistol for a small bag gun and I have compartments in my SUV that will easily store a full sized AR or AK plus several magazines. They can fill a role for some but I'd rather go with a rifle round in an equal sized platform. I think the main reason they sell so well is the fold-ability. Take that away and its not much smaller than an AK or AR plus its still only shooting a pistol round.
I'm in no way knocking it. Its a good gun,especially for the recoil sensitive but I'd suggest for someone to try and rationalize it before picking one up. Also, don't add a bunch of garbage on it since at that point you would be better off with an AR. Its meant to be a small stow & go gun so to make it bulky would be to lose the purpose of such a gun.
I kinda use to kid to people that it was a poor man's MP5 except you slap the bold down from the back instead of the front.
Please read: Nothing here is a bash on those who own and like the S2K. This post is one man's opinion. 