I've been more of a grip guy but is now also intresting in the gymnastic training. I will try to share what I know about grippers and maybe it could help some.
In the gripper community there is very different point of views of what is a called a "close" of a gripper.
* TNS - Total No set, means that you just grab the gripper with one hand and close it.
* CCS - Credit Card Set, its the way Ironmind(that sells the CoC grippers) certifies gripper closes. Meaning that you start the close from credit card width.
* Parallel setting - You start closing the gripper from parallell.
You can also work with chokers on grippers. It's a good because you can then open up the gripper to different widths depending on your strength. I have one video where choker used on grippers can be seen:
Regarding the widths on grippers, it differs a lot and it can a big difference in how diffucult they are to close.