I wondered when someone would attempt to copy a SmartDrive. This one doesn’t have any Bluetooth controls, and seems pretty basic in comparison to the real SmartDrive, but it’s a lot cheaper! (Although the minimum order quantity is 10).

https://wisking.en.alibaba.com/product/60849158497-803140643/Professional_Manufacturer_wheelchair_trailer_rear_ SMART_spare_part_for_disabaled_person.html

Unfortunately the very basic instructions neglect to mention how you stop the thing!

There is a video of one in action on the Alibaba app...but I can’t post a link to that.