I bought a Zefferus from eBay. Kept it on a couple of weeks and then pulled it off. Lot of problems. I mentioned them in another thread. Biggest was how it blocked seat movement. I'm 6'4" and 280, so I need every bit of room for the seat, and having the windblocker installed cut off about an inch or so of seat movement. And if I did scrunch myself in with the seat in front of the blocker, it rattled. Oh, and it also created a reflection that was pretty dangerous in the rearview mirror at night.

Took it off last week. Good riddance. I buy another one, I'm going to likely go for a mesh.