I have also done some homework on the Keyde/Tongxin motors. It appears they both come out of a project of Hangzhou university.
There appears to be a lot of concern about the reliability of these motors.
No big company seems to have used these motors which is concerning.
There's been plenty of past experience in this forum with Tongxin motors. Their first appearance was in the US Schwinn Pacific which was an all-round failure, the Tongxin set up for 20 mph assist in a 700c wheel. The first controllers often didn't last long enough for the motors to fail and we eventually saw an email issued by a Schwinn vice president withdrawing the product with the comment that it wasn't ready for consumers. A tiny number reached here, imported by Hilderthorpe Cycles, a small Yorkshire shop.
Used as kits by members, controllers originally also figured prominently in the failures, but a number of motors have suffered broken spindles and slip rings. Some members have gained the skills to repair these and created tools to assist with that.
These motors are most reliable in low stress small wheel applications, usually for lower speeds, a perfect example being the Tony Castles/A-to-B Nano-Brompton with assist to 13/14 mph in a 16" wheel. Mechanical failures have been more prominent in larger wheels, especially 700c.
Schwinn have since used them again in full size wheels with a very low power controller and the Toshiba SCiB low-capacity fast-charge battery, and those appear to be ok in that low stress application.
Cytronex have always used them, but an early enthusiastic band of about four members with those first bikes soon disappeared, so no idea how they lasted. One longer term and experienced member, HarryB, bought a Cytronex to use on his daily London commute and suffered motor failures. Eventually a replacement motor he was given by Cytronex he was very dissatisfied with, insisting it was markedly lower powered than previous versions. He eventually gave up on the Cytronex, swapping to another type of e-bike, but seems to be no longer active in the forum.
A few members who originally argued that they were reliable motors in their larger wheel applications have often been caused to eat their words later. Current members with them mainly seem to have them in small wheel, folder applications.