Outwardly there is little, if any difference, as far as the kits are concerned. The MkI had a metal hull, and served chiefly with the Royal Navy, Fleet Air Arm and Commonwealth navies, whilst the MKII, which served mainly with RAF Air Sea Rescue squadrons, had a wooden hull. The Airfix kit is very old and basic, dating from the late 1950's, although reasonably accurate in shape etc. The Revell kit is the ex- Matchbox kit, from the late 1970's or early 1980's, and possibly a better choice, although still fairly basic.Ii believe Matt 308 has a thread somewhere in the modelling section covering the latter kit.