It depends on how fast you want updates. I'm sure you know how Debian works, so if you install LXD from Debian 12 repositories you'll be on 5.0.2 LTS most likely for ever. If you install from Zabbly you'll get the latest and greatest right now.
My companies' machines are all running LXD from Debian repositories, except for two that run from Zabbly for testing and whatnot. At home I'm running from Debian repo. Migration from LXD 5.0.2 to a future version of Incus with Debian 13 won't be a problem as Incus is just a fork and stgraber and other members of the Incus/LXC projects work very closely or also work in Debian.
Debian users will be fine one way or the other. I specifically asked stgraber about what's going to happen in the future and this was his answer:
We’ve been working pretty closely to Debian on this. I expect we’ll keep allowing Debian users of LXD 5.0.2 to interact with the image server either until trixie is released with Incus available OR a backport of Incus is made available in bookworm-backports, whichever happens first.