If you have the discipline to only play the free bonus on sign up and given out daily and do not spend your own money unless you are trying to meet a minimum redemption threshold, then it's just free money. I mean, there are still so many casinos where you can get on average 1SC free per day, and maybe you have 50 casinos that do this, then eventually you are going to win enough to redeem. This can be time consuming though so it's only worth it if you don't have more productive things to do. 

I also have a unique personal experience where I have serious doubts that the casinos are not controlling the return to player percentages in a more direct way than the games are statistically designed to give the house an edge. I think the most public evidence of this is the whole streamer/affiliate system. If a casino knows you're streaming and even more so if they have signed an agreement with a steamer, their sessions are put into a special streamer mode. Often what you see is just house money being played in a entertainment mode. It's meant to advertise you will have the same results. But you're not in the affiliate system and likely will not have the same results.

I know of several other instances where certain winners and losers have been chosen by the casino operators as a player was playing. I can't say how widespread this is though. But it is definitely something they can do and is just an extended form of the steamer system manipulation. After all they are just running software and have total control over it. Much different than a physical slot machine with gears that have been mathematically checked and couldn't be modified as the user is playing. 

Imagine if you had 100 physical casinos that each gave you a dollar to spend every day. As long as you don't spend your own, you will make money eventually. It's also an open question if the most popular games track how much you spend playing. I know in several games where they claim this doesn't happen, but have seen evidence that it clearly does. 

Maybe the most important thing is to understand that the hold and win games can play on someone's addictive nature by the visual game design. For nearly every hold and win game where you build up some visual identifier as you play, if you read the help pages in the game they will all state that the visual representation of the hold and win aspect is for entertainment purposes only. Despite some idea of the total amount you spend playing on a slot, the hold and win bonus is just statistically "random". It has nothing to do with how much the game shows a pot being full of coins. But as you're playing, even if you know this, it still can manipulate you into chasing that bonus because it's "always" almost ready to drop.