I have an old set of Kreitler's that I used a long time ago (don't anymore). I just found that rollers require a lot of focus, especially the cylindrical ones like Kreitler. You can't really take a break, it's hard to adjust your position, you do have to concentrate on staying centered and your pedal stroke. I know the last part is good, but after a while, it gets tiring. Also, I admit I wasn't the most comfortable on them, and it was hard for me to get on and off of them. I actually ended up using them in a door jamb, in case my mind wandered enough to the point where I would have ridden off of them, and to help me stop and start, take breaks etc. I'm sure other riders are more comfortable on them, but I wasn't a fan. I'd rather use the monotonous (but safer/easier) trainer than rollers, but that was just me. Never used parabolic rollers, but I could see how that could make them a bit easier/better. I'd probably go that route if I were buying them today.