The TSO'd version has been through the necessary testing/certification program for it to be permissable in an N-registered non-experimental aircraft. In practice, this tends to almost guarantee its acceptability in a Cof A aircraft on the UK register.
Non-TSO'd equipment has not been certificated to meet the standards necessary for installation in a normal category N-reg aircraft, and may or may not be approved for installation in a G-reg. Check with your avionics engineer before fitting any avionics in your aircraft.
I don't recall there being any problem fitting the non-TSO'd KT76A in a G-reg but it would be wise to check.
2D