In terms of quality of workout, you may be better off with a trainer. The rollers' difficulty to master and lack of support may make it hard for you to do intervals, standing, etc.

Also, since it is harder to move around, shift your weight, etc., your butt may end up getting more sore than it would on a trainer. I have a friend who got rollers instead of a trainer and he wishes he'd gotten the trainer because his butt is so sore.

Just a couple of things to think about. Can you try riding some before you buy to get a sense for how hard that learning curve will be for you?