I had a tow behind rotary spreader and hated it. I threw it out to the trash but someone "salvaged" it before the disposal company arrived. The ground wheels engage the rotation shaft and if the ground wheels don't have enough tractions they do not work well. I got mine for winter salting but found it to be pretty much useless because of slick spots on the drive way. For fertilizing it seemed to do well when it was loaded down with 100 pounds or more of something because the weight of the material in the hopper helps keep the wheels spinning but as the material is thrown out of the hopper it lightens up and you lose traction, especially on bumpy or lose ground.
I am considering another one, but I'd only buy a PTO driven unit like the ones at Sweets or CCM. There is another brand that I've seen that is 3 times the price that looks to be more flexible in what it will spread, but I'm not sure I have the use for something that has the capabilities, I think the brand was HURD.