I've bought a kit, and an engine from zoombicycles. The first motor blew up after alot of miles(mostly WOT). I then bought a second one and have been using it since then. Seems good, and had good shipping pirces for me(live in Canada).
I did have some problems with the customer service however. I was trying to buy a chain and sprocket. They told me it was freeshipping and would cost about $55. When I went pay for it they tryed to get me to pay for shipping so I asked why and they said only engine kits have free shipping although I was told in two seperate emails the shipping was free. Anyway ended up going to bikeberry.com, after I told them I'm not going to take there false advertising.