Polymer TX22 FRTs available in 5 or 10 packs. The metal ones will destroy your gun, polymer ones are much cheaper although semi-disposable. You will need to completely disassembly the gun to remove the slide once the FRT is in - this is true for the metal ones as well. Each polymer FRT should last several hundred rounds. Design has been modified to optimize for polymer.
Click here to purchase a 5 pack for $50
Click here to purchase a 10 pack for $90