An additional issue with freewheels is that there are only low quality DNP ones available (from ebikes.ca) which have 11 teeth on the smallest cog. This is desirable to get up the gearing sufficiently high to be able to assist meaningfully at top speed by continuing to pedal. Shimano doesn't make 11 teeth freewheels anymore. As noted, almost all hub motors use screw on freewheels, except the CST Bafang.