Check out Sweet Maria's for a long thread about this popper. It's what I use and I'm getting good results, but I've only been at it for about a month.
Some of the suggestions are to stir the beans with a chop stick to keep them moving until they dry out. When they're green, they don't spin so much. Once they're brown they move better.
Another suggestion, which I've been following, is to shake the popper to move the beans around as they dry out. I'm doing this and getting a much more even roast. It also helps knock more chaff off the beans.
Some people have put a glass chimney on the popper instead of the plastic hood so that they can shake it better. I haven't done that. Yet.
Also, you'll get voltage drop if you're using a long extension cord or maybe a circuit with a lot of other appliances pulling juice. Apparently these poppers are pretty sensitive to that.