Rollers will help you spin a high cadence smoothly but I agree with Caloso, riding a FG of 70" in hilly terrain is much more fun and as long as you are providing force to the pedals and not soft pedaling.
Both techniques used in tandem will give you the ability to spool up the rpm quickly which is the real secret to a killer sprint.
The FG will help you develop the power while the rollers help you gain suppleness and leg speed.