1. Watch out for the availability of the electric control unit, which is a small circuit board, this one normally spoil.
2. Motor is quite standard, need servicing after approx. 1.5yrs to 2 yrs because of carbon buildup inside. Percentage of failure depends on OEM manufacturers quality, normally 5% failure rate after one year. Can be repaired if electrican knows his stuff. Life span about 4 to 5 years, normal wear. Normal practice is one to one exchange form the service shops.
Can reach speeds up to 50km/hr or more. Thats why banned on road. With that kind of speed capability, classified as motorbike by LTA (if my RAM serves me right

)
3. The rest are cables and soldered joints that can be easily repaired.
4. I recommend one with simple skeleton design, not those that look like scooter.
5. Ask what are the safety features of the product. e.g. Rider may have to paddle a few cycles before the electric supply kicks in to provide power to the motors. This is to prevent bobo kings who accidentially turn the throttle and surge forward into passing traffic at traffic junctions etc.
Thats where the ECU mentioned in item 1 is critical.
6. If you drop the bike, fiberglass body may break, that's why I recommend one with simple design.
7. Any simple manufacturing setup can manufacture this class of products, so dont be surprise, manufacturer close shop after afew years.
It is just buying the items and putting them together, with some simple sizing of the electronics.
Again, built in safety features is important.
I hope that forummers can share their experience on electric bicycles. Where can we buy good electric bicycles with strong backup services in Singapore? Price? Lifetime and cost of batteries? Which are the better brands? How about the foldable ones with Lithium batteries? Should I buy from China?