I've never bought from them. I didn't see anywhere saying factory Yamaha parts or such. It's not a bad price, but I think you could spend that money better. Using that kit on ebay will not allow you to run the web.390. Simply because the valve springs are going to be stock type, not high perf. Also the rocker arms aren't hard welded. It will cost you $65 each for the h/w rockers,valve spring kit w/aluminum retainers $72/$95 for the titanium retainers, and the cam is $148. That's w/o core charges, according to web's website. So you can see where I'm going with this. If money is an issue maybe consider going with the stage1 hotcam. When you compare the specs side by side, you'll see web shows their specs in sae, and hotcams in mostly metric. Convert the metric to sae and you'll find the hot cam has .002" more lift (ok not that much more) and it has 250 degrees of rotation at .039" of lift. That's 6 more degrees than the web at .050" of lift. The only other diff is the lobe centers are slightly more on the hotcam. So they are very close to one an other. I have the s1 hotcam, as do many others on here, and have been very pleased with it. I am also running stock valve springs and have not experianced any problems w/valve float, and I run my bike wot throttle for a fair amount of time on all the logging roads I have around here. If your valves aren't burnt, rocker shafts aren't worn, blah blah blah, you don't need that head rebuild kit. Just my .02.
