Yep, you'll have to get a lighter recoil spring or run mini mags through it.
It is however, not actually manufactured by sig, just branded... or so I'm told... hence the lackluster quality. Not a huge fan of .22s but imho the p22 is better.
Some Mosquitos do fine, especially with the factory-recommended CCI ammunition while others don't have much luck at all regardless of what ammunition you use. Occasional FTFs and FTEs are not uncommon for most .22 semi-autos regardless of the manufacture as there is just not a lot of unused energy in the round to also cycle the slide. My Mosquito works well with CCIs but does have an occasional hiccup with bulk .22 ammo. Actually helps with my clearing drill (i.e., Tap -- Rack -- Fire).
I really love mine. I like the looks and feel of it.
Secret to having the Mosquito run all ammo. Polish the feed ramp, open the chamber ever so slightly, and stone the slide rails & mating surfaces, making sure there is no paint or burs.
Love mine and have had absolutely no issue with it. Keep in mind if you want to buy one, that they like "hotter" ammo rounds, as in high velocity. The muzzle velocity of the round in question, will enable the slide and feed to function properly. Sig recommends the CCI mini mags but other ammo of similar muzzle velocity specifications work more than fine. I would recommend going to Target Sports USA | Discount Ammunition Online | Ammo For Sale | Free Shipping Ammunition and peek around at the various .22 ammo types. This site is great for posting the characteristics of ammo so you can compare and contrast and get an idea of what types the Skeeter will fire. If you buy cheap bulk stuff, the chances are they will not have the proper MV to allow your pistol to function properly and IMO this is not just the majority of issues experienced and posted about all over the net for the Sig Mosquito, but also that of the .22 Tac Rifles/AR 15 clone-wanna-be's out there.
If you dont want to spend the money on high velocity ammunitions for either of these firearms, purchase a "plinker" six shooter and a Henry Rifle. From my experience they both shoot just about any 22 LR cartridge.