grippers develop crushing strength, not grip strength. they're not the same thing at all unless you train with grippers in a particular way (rather than doing reps you do a full or partial close and hold it for a minute or two).
if you want to develop grip strength you can do heavy DB/BB holds, plate pinches, farmers walks, etc.
for me, the only thing I do is NOT use straps on anything. eventually your grip will develop on it's own once you start holding on to heavy weights for a minute or more at a time.
honestly most of my grip strength and forearm size came from raw deadlifts. like this:
http://youtube.com/watch?v=vEVMDIRHe9A