Locked-down Games
It's playable, and fun to use, especially if you phone your opponent. My family and friends have been using it quite frequently during the lockdown.
It is NOT robust.
It is really easy for dickheads to ruin games that others are playing.
No attempt has been made to stop denial of service attacks.
It's probably easy to crash the server with malformed data.
Many games are based on trust. If you want to cheat, it is easy to do so. If you are a programmer it is easy to see other players' cards/tiles, but there are easier ways to cheat too, such as dealing yourself extra cards/tiles.