Met a bloke from the UK who laughed(out loud) that I logged my flight time in decimals and not in hours:minutes.
Aside from him being a knob, it doesn't matter what format or style your logbook is in - it's your record of
your flying hours.
You could log all your private flying in a pocket diary or a school exercise book, or on the back of beer coasters, provided that you correctly annotated the time as dual, PIC, single, multi etc. and the aircraft rego, route etc But if you already have a CASA style logbook, that’s OK.
Exactly as Mach E Avelli said.