The features they have included, mostly, and complete lack of any KYC needed.

They have:

Nostr Wallet Connect

eCash for privacy

Lightning address for receiving zaps

BOLT12

Easy to use UI

And I am sure I am missing something.

As always with custodial solutions, you are absolutely at risk of being rugged, so don't keep much on there.

Personally, I am using Alby Hub on my own Start9 with a parallel CLN node for BOLT12, so I have all of the above features, except the eCash part, completely self-custody. For those who just want an easy custodial option, though, it's hard to argue with what nostr:nprofile1qqst4qyeqenw7zm0fwjsty68h6cnys5jre2xd8ngqpjv5a2j26s78fspzemhxue69uhhyetvv9ujucm0d9hx7uewd9hj75a0pev has going for them.