8mm is a good size, for most pigeons. Larger size for pigeons with feathered feet. Or for larger pigeons like King Pigeons.Awesome, thank you! Do you need any special tools to put them on? I have jewelry plyers of various sizes if pinching them on with my hands won't work.
Also, do you think 8mm is a good size?
The bands you linked to do suggest using a special tool. It is quite pricey.

$90....... ouch
I would make area I highlighted in yellow, SMOOTH, not serrated. This way it does not deface the outside of band.
Your second option are the plastic snap on type. These are reasonably priced. These are from a US seller,, so arrive quickly. Those from China Sellers are less money,, but delivery is longer.
In the past,, I used the BLUE, and the PINK to ID my pigeons' genders at a glance. It helped since all my pigeons were white. (and plenty of them at times).. This was in addition to their permanent bands on other leg.
You can make these plastic bands more open-proof, if you dab a drop of SUPER GLUE into locking joint.
Get one of these engraving tool and scribe whatever information you desire. Most peeps just put their contact phone number.