I buy from him when he is cheapest, or close, and elsewhere when I find things significantly (for me) cheaper, which has been more often. If you compare with UK suppliers, especially those 'local' in Wales and don't want to look at other eBay/Hk sellers then of course he will be cheapest most of the time. Your choice. I'm not tied to any seller or locality but look at maybe 4-5 consistently ... including Ian.
EDIT: one thing to add at the moment is that with UK rebates Ian is pretty much unbeatable on lenses and bodies.