Most platforms out there allow you to play for free. In my experience, all of the payouts are the same as the real play(and the casinos obviously state the same). I dont believe there to be conspiracies of casinos tweaking the payout odds so that free play payout out better, though I imagine many people would like to believe that.
Either way, whether the odds are different or not, it still makes sense to play the games that you are promoting, especially if you can do it for free, so that you have a better understanding of the products that you are promoting. This can also be a benefit to you if you realize that a particular game is a lot of fun, and a casino is running some kind of rewards promotion on that game…you can then promote that to your clients.
My 2cents at least