For grip training I never use straps. Also I do very strict wrist curls and reverse wrist curls, for sets of 6 as heavy as possible, 3-4 seconds each way. Heavy Deads with no straps as well as slow, weighted chins have built my grip up very strong. In fact, when I used to use straps for everything I struggled to hold 315 for more than 3 or 4 reps, now grip is never the limiting factor which is a bonus.