Sounds like you are referring to what we call friction drives. They don't work well in wet conditions. My personal experience tells me that they are not reliable at power levels over 1,000W. If you are happy with 750W, 20-MPH, and mild acceleration...a friction drive is definitely an option. I would never use one for off=road, since they work best on a smooth tread tire.
A narrow demographic, but if that sounds like you...I was happy with mine while I had it. I most liked how I could easily pop off the seat without any tools, and carry the electric drive indoors or up stairs (since mine was attached to the seat-post).