That's a pretty common reality, you don't generally buy glass & get diamonds.
I have a friend & that very easily could have read I had a friend... I have a friend who wanted to build an eBike & felt he could save some money. He got parts from a bundler out of Canada & the parts all came from mainland China. The Canadian company orders a bunch of parts from China then "builds" kits with emphasis on the kits being from Canada even though ALL the parts are from China.
Anyway, I helped my friend mount his wheel & rig his wire harness but, I refused to connect his battery I didn't even want to be in the same zipcode when the connection was made. He had another friend who has a background in DC circuits who helped make the connection because this fine Canadian company doesn't even put terminal ends on the battery to motor wires... you have to make your own, hope you don't mess up when you figure amps & ohms.
Well I get a text today telling me the motor blew & the kit is a total loss. Hopefully he put it on a card that guarantees the stuff he buys with it so he can get his money back because the folk at that fine Canadian company seem to never answer their phone. If it had worked he would have had a kit that was arguably stronger with more stamina than mine for about 1/3 the cost of my kit. One of the things that sucks most about growing up & becoming mature is "I told you so" just isn't fun anymore. I'm nearly as bummed out about it as he is.
The Canadian kit in question is NOT not NOT from Bionx, they're too slow is the only thing I can say against a Bionx kit. They do have a 28 mph kit now for those who might enjoy a rear wheel kit.
So when building do your research, drive around test out the 3 different placements for motors rear front & bottom bracket, see which one you like best. Buy a motor from a reputable manufacturer that isn't just bundling Chinese parts from utterly unaccountable vendors. Spend a few more coins up front to save yourself ... well it may be just that simple, to save yourself... & a headache is the least of the things you'll be saving yourself.
I don't know what went wrong with that motor, if the battery was dangerous, if the controller was defective or the motor was bad... I guess it could have been as simple as bad bearings but, I doubt it was the bearings.
More about that fine Canadian company, they don't send any instructions with the kit (they did have the money to buy heavily branded boxes for their small parts packages) the instructions online are for the rear wheel only & the YouTube video is not as helpful as I had hoped, the guy who took the time to make it should be thanked for trying.