Considering he didn't say self-custodial, that's likely the catch

https://github.com/getAlby/jim

It's just albyhub, modified to be hosted in such a way to operate as a custodian for others, rather than run for yourself.

The catch is, it's custodial, and you get no contractual protections at all. Honestly, probably fine for throwing around a few thousand sats at a time, but at the end of the day, it's an onboarding tool someone seems to be hosting for free because they want to see Nostr gain adoption.