I’ve never used split metal bands. I use plastic snap on ones though which are another option outside of permanent bands so I’ll offer my opinion on those. People have gripes against them but they’re certainly better than an unbanded bird. I use them. They are less secure than closed bands because they can be removed but this is a difficult process and they couldn’t just fall off on their own. Another benefit of the snap ons is that they are easiest to manufacture , making them the cheapest option if you want them custom compared to split or closed rings
When I miss the banding window for my birds they just get a snap on with my phone number on one leg. The ones that do get their AU bands also get a snap on with my phone number anyway, to make it easier for someone unfamiliar with reading pigeon bands to contact me.
8 mm is a good size for homers