On my opinion, it doesn’t make any site slower.
They only have to check it once, which is when the visitor click on the content link to visit the casino.
There will be a database table with currently about 110,000 records with all IP addresses. Each record have IP_FROM and IP_TO, and the country that the IP range belongs.
One search in the table to compare the visitor’s IP and the corresponding country in the table and you already know if it is a good customer or not.
If it is not a good visitor, one more search in the database to fetch a possible bouch back url of the affiliaie and redirect to it.
That is it.
I’m pretty sure many casinos already do the first part as it is… they only have to implement the second part.
Also, I believe that many times is not the casino will be implementing this but the affiliate program.