I have used them in a door frame, too. It helps.

I have an exerciser attachment that goes under my back wheel with a small roller and a fan cage. There is an adjustable post to support the bottom bracket. Another post attaches to the fork. It was a pain to take the front wheel out and hook the exerciser up to the bike, and then reverse everything if I wanted to ride. I thought rollers would be the perfect solution. But, I have found the rollers difficult.