Medway Boys Protector III is the blue one. It works for me with TOS 1.62, 1Mb, STE on STEEM 4.01
Protector III was very short-lived. It was supposed to be the last one but shortly after it was released 3.1 came out.
Medway Boys Protector IV was the best. It was the purple one.
Still got, still working: Atari 4Mb STe, 520STFM, 2.5Mb STF.
Hardware: Cumana CSA 354, Ultimate Ripper, Blitz Turbo, Synchro Express II (US and UK Versions).