There are uk suppliers and people have used them with good results. As with most things you get what you pay for. The cost of the pro kit I have when you break it down is amazing.
Turbo on its own 1400, wastegate 400 ish I think, bov best part of 300, oil and water lines and fittings couple hundred, down pipe with dump tube at least 150 to have made, massive hand made intercooler 200 or so, couplers and claps 50. Then you're getting a hand made life time gauranteed stainless manifold and alloy ic pipes. When you work out the cost of the buy in parts and materials they are near enough doing the fabrication work for minimum wage. Add to that the exchange rate is a good bit in our favour. It's not a bad deal.
All that said mate, you can't just buy a turbo kit and bolt it on then expect it to work. There's a lot more to it than that. If you build the engine expect to be about 150 quid in oil and oil filters alone before it gets to the dyno.