Operating under VFR, either in Class D, E, F or G airspace in the UK you may well be in a regime where other traffic is carrying non-Mode C SSR. Or even no SSR whatsoever.
Thus you might receive an RA about someone 400 ft above who you can see isn't any real problem. But you react within 5 secs as taught and descend into someone you didn't know about.
But of course you cannot simply ignore RAs....
Whereas TA only forces you to look for ALL other traffic in VMC before manoeuvring appropriately. Presumably you will be in receipt of a Radar Service (either RIS or RAS) when operating the sort of small turboprop for which the TCAS mandate will apply? If so, ATC should be able to back up a 'Traffic, Traffic' advisory.
There's no obvious solution; however, I think that a habit of ignoring 'nuisance' RAs in Class G airspace would be very unwise indeed. Perhaps better always to use TA/RA in IMC, but to use TA only in VMC even under IFR with a RAS/RIS?