If you're just converting a freehub to a singlespeed all you need is a sprocket that fits, and doesn't have the cutouts that help the chain come off the sprocket (when changing gear in its original application). It's basically a flat piece of metal in the shape of a cog, so no point in spending £££s! I doubt the ones from China would be significantly poorer in quality than a £15 one, they'll just take longer to arrive. Imho