Most of the time if you really want to see what a real slot is like, and if you will like it or not, drop it to minimum you could gamble and play 10k rounds if you can, obviously sometimes it is too high and you can't play it, but if you can afford to you should do that because under 1k
I think I can get a clear opinion on wether I like the slots or not simply from testing the bonus feature without having to play 10k rounds. What matters the most for me would be the bonus feature, I personally dont really care about the base game at all because I tend to either use the turbo mode or do another stuff while I roll
Even if you are a fan of the base game, simply look for the slot review videos on youtube instead of rolling 10k rounds.
I personally have never won anything good on Deadwood, but that's probably because I played less than 100 spins on it overall. Almost all of them were losing ones or with a small payout.
Deadwood's base game is probably the worst I've seen as well and its pretty rare to land 3 scatters on Deadwood but the bonus round could be massive though. Idk though I rarely roll on Deadwood, I always go straight to purchase the bonus round whenever I play on it