My experience tends to mirror veganbikes experience.
Soooooo, I own an ebike store. I AM the only guy that will fix or attempt to fix odd brand e-bikes.Those odd bikes of course are from China. So many different brands have popped up over the last few years. Some of them look exactly the same, but dont be fooled!
Lets take Rad to start with. An early customer came to me with problems that I was able to fix on his wiring. This was after he hounded the company for a new main harness because of erratic behavior. Next was a guy who was sitting in his garage when the fireworks went off. His main harness made lots of smoke and sparks. That problem led to killing the controller, the throttle, the display, and one brake lever switch. SInce then I have also replaced many other controllers and displays. THEY GO BAD! And this is from a brand that thinks their product is reliable. And their customer service is staffed by idiots. I will not deal with them for parts. the customer can get them. They even hired a guy to take care of problems. He did do me good for ONE repair. then he left on vacation!
Amongst the others, I regularly replace controllers, throttles, PAS sensors, chargers, and batteries. Many times the repairs are something stupid like a bad connector. Other times they are much more difficult to find. Then throw in the Chinese seem to be color blind. Many components do NOT follow "standard" color codes. Still others have connections in different places and I have to do connector releases and push them back in other locations. Some of these companies are impossible to communicate with for spare parts. Still others have wacky prices for them. Some just do not have spare parts. So while I play the game of 20 questions through email and send reminders that I have not received answers the customer waits...and waits...!
The only job I do I cannot blame on the manufacturer is a severed cable on a motor. Even some of these are semi simple and others cannot be accomplished without hall sensor replacement.
Then lets switch to the reputable brands I sell- I do... tune-ups. Flat tire repairs. Gee all the normal bike stuff! Occasionally I get a warranty repair, but those are few and far between.
No I havent kept count to give you REAL statistics. Its just what I see being THE GUY who will fix a non branded bike. Sure there are people who buy these and have no problems. then you have that one person who gets their bike wet and the switches short out and kill the display and controller.
Theres a written account of my life at the bench. That should back up my opinion.
-SP