1. Easy retrofit for existing bikes
"That might be the easiest ebike retrofit/conversion I've ever seen." – kiddico
2. Small battery & limited efficiency
"Most entry-level ebikes have at least 10ah * 36v batteries; a few lightweight models have 7ah. So this has about half the battery capacity of the cheapest ebikes." – fwipsy
3. Theft vulnerability
"Thieves will just take the whole bike." – SoftTalker
4. Legal/Regulatory framing
"There's no restriction on manufacturing e-bikes anywhere that I know of, as long as they obey the speed/power limits." – IshKebab