My thoughts on the xiongda 2sp motor.
I bought a 36v one direct from Xiongda, Bonnie was great to deal with. I got all the options because why not, they're dirt cheap. I sent Bonnie my rim dimensions and she added 251mm spokes for $8, how can you pass up pricing like that. I think they're 12ga so pretty burly. I built my wheel and put a bike together and rode it for 4 months over the summer. Even in 35 degree heat climbing a 5 km hill flat out pulling 450-500 watts I had no overheating problems. It developed a squeak I was unable to pinpoint but I blasted the entire hub/cassette with some Teflon lube and it stopped.
In the fall I put it on a bike for my daughter to ride at university. She rode it all winter with no problems other than the squeak came back for a while but eventually stopped before she came home for the summer. The display shows 720km traveled.
It is not a fast or as powerful as my 48v Bafang bbs02 but then again it's only rated at 350w compared to 750w. For a 350w motor it packs a lot of torque. It climbs well but it's speed tops out at about 32kph. Being only 350w it goes a long way on a battery charge.
A friend bought one from Luna and asked me to build it for her. All I can say is buy from Bonnie. Luna's cost $200CAD more (delivery incl.) and didn't come with brake levers or spokes. There was no option for different configuration (disc, no disc, cassette, freehub, colour, cable length) so she ended up with a disc brake compatible freehub style that is too wide for her dropouts. Fortunately she's got a steel frame so I can make it fit.
I ordered another for myself today to put on my recumbent. I got extra brake levers with electric contacts for my friend's bike for $5/pair while I was ordering. I ordered the 48v one this time so I'll post a comparison of 48v vs 36v soon.
As for the rolling backwards issue, occasionally when I rolled it backwards it wouldn't turn. A little rollforward then back and it would usually go. When I was building the wheel in the stand it would never roll backwards. Now after 720km it rolls backwards every time. The new on I'm building is in the trueing stand right now and turns both ways no problem.
Edit: Follow up - 48V motor has more torque than the 36V motor obviously but more than I was expecting. The top speed is only about 4kph more at 48V though. The brake levers I got direct from Xiongda would not work with the Luna kit, The Luna provided sensors are normally closed contacts whereas the Xiongda ones are normally open. I asked Luna if they knew of any way to make them work but got nothing from them.
Edit 2: My 36V motor sh*t the bed yesterday. It works in low gear but in high gear I hear the motor turn but there is no propulsion. I guess it's time to rip it apart and see what happened.
A friend bought her 2 speed motor from Luna, it doesn't have automatic shifting and it's kinda inconvenient to shift from high to low, you've got to cycle through the assist levels up through #5. Once in low you've got no varied assist. She is not very athletic (being nice) and overworks her motor on the hills in high gear and it overtemps and cuts out. With the auto shifting I've never had mine cut out.