AFAIK pppoker is legit. I haven't tried playing it but I have seen my friends playing it and advertising it through their profiles online. I don't know if there's an incentive if they manage to make their own clubs with many members, maybe there is.
Looks the domain is real coming from betking and advertising his club as an advantage using the database of registrants through betking, if you trust him, you can join his club but if you don't, look for elsewhere that you trust more.
PPPoker is indeed legit. I've played it several times with my friends and I had issues yet. But what bothers me is that after reading this:
On a side note, for you info betking.io has partnered with one of the reputed gambling sites bitsler. They have refunded all the account which had their criteria(Maximum- $200). You can check more here-
https://bitcointalk.org/index.php?topic=5241045.0 ... and checking the link, I'd seen his profile having trust flags that was too alarming.
If the makers of BetKing has something to do or had cooperated with pppoker, I might consider stop using the game. I'd rather choose other gambling platforms than risk on something that might have connection with a scam project. Also, them sending you an email is still alarming as well, whether if it is for promotion of other project or not. It must be deleted in their database, yet somehow it was still used.
(in which they can still have your credentials as well...)