You probably won't benefit from changing the oil too often, there's even been some articles explaining why it's NOT good
to do it too often (didn't pay much attention to explanation). Just stick with the recommended oil
(usually 5W50 for the G5 300cc engine) and you'll be good with the recommented 5kkm intervals.. but it's probably better
to change it 1000km before then 1000km too late.
Then again, I've seen an Agility 50cc that blew up at 28.000km because it ran out of oil, the owner NEVER changed or
checked it, it would probably be still running if he at least topped it off. Not that I'd recommend doing that.