Both versions working for me:
add:
With the first solution ($users->add) you’re adding users to the existing kirby user object, so you can kind of mix users from DB and Accounts. e.g. admins from accounts and editors from DB. but you have to check/add users in different situations, by your own.
extend:
Second solution is replacing the kirby users object with the extended on. so the accounts folder is not more needed, and all users are from the DB source. i think this is cleaner because all users are from one spot and you have all users by initiation.
Panel works in both versions, also frontend login.