Their has been alot of chatter about this in the forums for the past year or so. Almost all Microgaming casinos now run free by-hourly slot tournaments that are free to enter for real money, like 32Red, Nedplay and Spin palace, the prizes arent as good as 3Dice casino tourneys but the point is that to cut down the amount of money won by players the casino uses robots to play, they dont even try to hide this fact, if you look at the usernames of these robots they look something like this
as you can see this is an example from Nedplay casino and you will see the same sort of thing happen at pretty much all online tournaments from microgaming casinos. Also they have rebuy features to join back in at a cost, so its not really free, you pretty much have no chance of winning at these tournaments, even if you place you will only win a few pounds after they convert from dollars to pounds..
If you want to play real free slot tournaments that give you a real chance to win real money from no deposit then go look at 3Dice Casino, they run proper hourly tournaments that are not at all hard to win, infact they are easy to place in..Go to 3Dice now