Engine flush and similar engine additives

Hi, I have a 2011 Astra H 1.4, and it'll get periodic maintenance soon. For this service, I'm thinking about using an engine flush for the engine — I don't think it's been used before. I've read online things like 'if you haven't used it regularly before, it won't help' or 'you need to use a rinse oil after the engine flush, otherwise it's useless.' The car also runs on LPG by the way — do you think there'd be any harm in using it?