Taking Bob Vogel's recommendation on which CoC gripper to start with is like asking Jerry Miculek what weight to use for a DA revolver trigger: they're both so far outside the realm of normal strength levels that you can't even see where they're standing from here.
ETA: I've been working the Flex-Bars since Tuesday. I'm shocked at how much improvement they've made in my elbow tendinitis in only ~3 days, and I'll definitely be using them for some of the many other exercises available on the Theraband website. Highly recommended as a means of preventing elbow tendinitis when used in conjunction with other intense training.