I just bought (it's on the way) a 50cc from them. After pricing them on ebay and whatnot, I found them to be pretty reasonable. The 50s I saw generally ran 150 to 170, then there's the shipping charges. The Dax was about 30/40 bucks more, plus shipping.
The guys there make sure the castings, studs and build are all good. This peace of mind was worth the extra money to me.
I also requested a 48 tooth sprocket (for my 29" bike) and they substituted it into the kit (no charge) saving me a few bucks there.
I won't receive the engine til Tuesday, but I'm not worried that it won't start or has anything serious wrong with it.
Duane told me the crank was balanced and all the bearings are the good stuff.
I doubt they are manufacturing parts, but they do select the good and reject the poorly made stuff so you get as good a popper as possible. Worth a few dollars more, no?