I’ve used it. I held my nose and bought a Urbit ID and got on the network because I really liked the idea and wanted it to work. The onboarding process for normies to get on Nostr is challenging but for normies to get on Urbit is completely untenable. Then when you finally get on the network the experience is very underwhelming. Very limited apps, not a great chat experience (chat seems to be the main app). I tried to setup the Bitcoin wallet, the documentation was incomplete and out of date. Nostr is already a much better experience for chat and private messaging and I’m going to guess that Nostr now has more users than Urbit I don’t see myself investing any more time into Urbit.