Please remember they have four casinos with free play offers so you are going to find a lot lower conversion. The downside of free play offers is that if they lose they tend to leave. If they win they tend to deposit.
Rewards tend to have a higher download rate but lower conversion to real ratio for us. But once they have them they tend to keep them so I would persist with this program. If you send that same traffic to numerous other MGS groups you are going to see little or no improvement.