those strap on chain cleaners are useless
I have one of those plastic chain cleaners with a weird brush system inside
it's a bit of a pain to use it but with a good dose of degreaser inside it it cleans the chain pretty well after it has been wound through it 8 or 9 times
I then wash off all the degreaser using a big bucket of water
then a good wipe with a cloth to dry it
during this faffing about I have the bits of the derailleur sitting in a bowl of degreaser
seems to work - the bike is massively smoother afterwards
GT85 - to get back to the point - I only use that (or WD40) in the winter as a quick fix after a wet ride when it is too wet or cold to clean stuff properly
I generally hose the mud off and dry the bike with a leaf blower (wife won;t let me use her Dyson hair dryer so some reason???)
then spray some GT85 over the chain and gears