im looking in to invest on a roto start with a cord less drill im just buying the back plate to replace a pull start on my duratrax nitro evader st .Is it worth buying? will it really give me fast starts

You are MUCH better off to get a start box. You can always pick up used ones for fairly cheap and new ones aren't that expensive to begin with. It will save you a tremendous amount of headaches.

starte boxes are more 4 racers im more like a back yard basher and front street racer