I guess if you are looking to practice on the cheep for the 229 or 220 you already have in a "real" caliber get the one that matches. I have carried the 229/228 in .40 and 9mm daily for duty over 20 years and absolutely love it. I have not seen the 220 in .22 cal.
My biggest concern would be how finicky they are with ammo. I have a Mosquito which is a nice little .22 but have heard others had ammo issues. I have never changed the buffer spring (to the included lighter version) and it works great. It is not as accurate as my High Standard but good for teaching the "boy" CQB and presentation from a holster until he is ready for a bigger caliber. You can't go wrong with any Sig product, but you pay$$$ dearly for the name.