You might obtain more answers if you post in one of the A level/sixth form college parts of TSR. This bit of TSR is about the University of Oxford.
As you may have gathered, there are several commercial outfits which seek to trade on the name Oxford, and their quality is likely to be very variable.
If something doesn't look and feel right, then it probably isn't right. In many contexts, you get what you pay for, and if something is cheap it may be cheap for a reason.
A company which operates from an offshore jurisdiction such as Gibraltar is obviously doing so in order to minimise taxes and maximise profits. There is nothing inherently wrong about selling education for profit, but some places are just cynical profit factories, while others actually try to deliver a good product.
I know nothing about any of the commercial providers of A level courses, but I suggest that you don't allow words such as Oxford or Cambridge to influence your purchasing decision. Maybe look at places near to your home.