TCM 22 is a conversion from 38 super or 9mm made from .223 brass, so at minimum you have another more common caliber to fall back on. Brass can be formed and bullets are plentiful, so even though it's usefulness can be debated, it's about as practical as it can be. 5.7 is more powerful, has a slimmer case, so more can fit in a mag, but it's proprietary with few firearms made for it, and the length makes a handgun grip huge. have fired both. There is a lot of flash/blast, but not much recoil, they are accurate, but being the FN is purpose built, and a more expensive pistol, it is more accurate, even if the trigger is worse than the RIA 1911 I tried. Plenty of debate on weather the ballistics are any better than decent 9mm or not and if it's all worth it.
The neat thing about the RIA 22 TCM pistol is they sell a set up with a 9MM barrel as well. Priced pretty nice too. I've sold a bunch of them. Rock Island also sells a bolt action rifle chambered in 22 TCM !!