Rollers have changed my handling of my bike more dramatically than any other training tool. I've had them for just around 2 months, but saw huge improvements outside, after just 60 minutes on the rollers the day before. As far as a training tool used for resistance, they're good for Zone 2/3 efforts. Actually, ideal for zones 2 and 3 because of the stability requirements, smoothness of the upper body and smoothness of the pedal stroke you need in order to maintain a solid Z 2/3 workout.

Also, I work on riding with no hands as that helps my ability to do so outside. Why is this beneficial? Ever need to put on a jacket, fix your junk, or do other things that require both hands, yet you don't want to stop riding? I ride out of the saddle on the rollers. This has really helped my out-of-the-saddle skills tremendously.

I've only put around 20 hours on the rollers to date and words cannot express how much more stable I feel on my bike, or how much more smooth I have become. It's not a placebo-effect.

I have a Cycleopd Fluid 2 as well, but it's reserved for higher resistance workouts. Also, it's more consistent in its power curve, so when I want certain targets, I'll use that.