By "complexity" I meant that they are "opaque" to me and somewhat not tied to and identity (be it email or username). Maybe it's me being inept, but I used them once or twice just for fun in Bitwarden and now I can't find them anywhere in my vault.
Perhaps a Bitwarden issue. I had them in 1Password and used them without any problems, then moved them out and into my Apple Keychain to separate those concerns a bit better. Both solutions work pretty well.
Having to pull my phone out or go and find/fetch it to grab a pin is pretty annoying for me, since I also don't keep them in my password manager.
I did for a long time but figured that if my password manager was compromised I would be royally screwed since they'd have my 2FA there to, meaning the password manager is actually a weak point.