Rollers have never failed me in the strength department really. Sure I have less resistance than with a trainer, but I do come away with a 32mph average after a good hour long workout on the rollers, dripping buckets of sweat with sore quads, so they are doing something. That being said, I do now vary my winter workout between rollers and a trainer. Two days strength training on the trainer (its better for intervals) and 3 days on the rollers practicing my spin and technique. I really like that the rollers take some concentration and also give my upper body a little bit of a workout--I can tell on our group rides in the spring who has been on rollers and who has been on trainers. The guys with huge legs and zero efficiency that are weaving like its their job are the guys on the trainers... the guys on the rollers however are smooth and efficient, though maybe not as powerful through the climbs and sprints.