Probably it's best to practice on a few registers which are already documented. The tool is not hard to use, you need to select the register address, then hold the shutter pressed halfway, and write down what happens. If you see the image flickering, then you'll have to find out what that flickering means - that's the hard part IMO.
Even if you can't figure out, you can simply mention that image flickers when you change the value in that register. This just means the register actually does something on the image and requires further attention.
The most time consuming part is to find out what registers are actually used. A lot of them are not used, and because of them, register analysis is effectively like looking for a needle in a haystack. Marking what is not used will greatly simplify this task.
About working groups... I'd say this can work well: pick some registers which were not documented, and document them. This means the next person will not pick the same registers, because he will see that somebody else already documented them.