tl;dr: avoid silicone, cheap metal is probably fine, plastic is hit or miss, but can be sanded if there's rough spots.
So, started off with a silicone cb-6000s knock off. It was fine but would chafe like crazy. Couldn't wear it for more than a few hours without adding some kind of oil.
After that, I got some silicone cage with these hard plastic rings that would snap in, and had a ball seperator. I forget what it was called, I think some people from HT or birdlocked tried making it. It sucked, it would break, and they stopped selling em.
After that disappointment, I bought a legit holy trainer, I believe a v3... Ir was still using the burg watcher me/2 style lock. Anyway, that cage was fine, but it was too solid, which made it hard to keep clean. Over all, it was fine, but there was a plastic seam down the middle. It was fine at first, but after a few days it would become uncomfortable. I fixed it with some sanding, but it changed the look of the cage, and I would expect it to be vibratory tumbled from the factory to remove the seam / for the price.
After all that, I tried a cheap metal cage from amazon and loved it.After finding one that fit me well, I took measurements and got a kink3d cage (a slightly more narrow cobra s) which is what I normally wear. The bars on the metal one were a bit too open, so there was a bit more feeling making it through. The kink3d one has the right balance of cleanability and isolation. Its also 3d printed so there's no seam line.
Comparing the kink3d to the metal one, both are good, and better than all the other ones. The metal one would very rarely pinch when putting it on, but otherwise was slightly more comfortable on my skin (only very slightly though). The main reason I like the cobra more, is that its lighter.
For both the metal one and the cobra, I would put a bit of oil on to lubricate it when putting it on. I might need to add a small dot more of oil once a day with the cobra, and maybe once every day and a half to two days with the metal one.
For oil, I just use refined coconut oil (if it smells like coconut, its not refined and will go rancid with your body heat). Depending on the temperature it is, I will add a few drops of jojoba oil to the coconut oil. This lowers the melting point, allowing me to get the coconut oil to be at an easy to squeeze out paste like consistency, which I keep in a small squeeze bottle.
Hope that helps!