I used Royal Purple 5W30 a lot in Australia. Here in the UK trying to find Royal Purple oils is like looking for a needle in a haystack, and when you can find it, the price is high due to import costs. Not anymore! Rival Motorsport are my Go-To supplier of Royal Purple and the price is good. Buying Royal Purple is a no brainer when garages sell their store brand oil (Tesco, Morrisons, etc) for a higher price.
There are a lot of great quality engine oils out there, each with their own community of supporters, so the choice is bewildering and very subjective. So long as the oil meets or exceeds the SAE rating and is the correct viscosity and flow you will be fine, especially with more frequent oil changes at shorter intervals than the service book recommends. Just remember that Royal Purple are American, meaning the oil comes in 1 Quart containers that are about the size to our 1 L bottles, but a quart is 946 mL, not quite a litre.
Rival Motorsport may be aimed more at performance vehicles and track racing, but if Royal Purple is good enough for the track it is more than good enough for a 25 year old Toyota Corolla. Combined with a Pipercross panel air filter the Corolla runs noticeably smoother and at lower revs than before. Before Royal Purple and Pipercross upgrades the engine ran at 3,500 rpm doing 70 mph on the flat, but now runs at about 3,200 rpm. Lower revs for the same speed mean less wear on the engine, thus extending the life of an already excellent little 1.6L engine. The difference is subtle, not night and day, but definitely there.
This is more a suggestion than improvement, but how about selling Royal Purple merchandise like shirts, fleece tops, etc.?