It amazes me that it's legal. It's clearly gambling.
I played a bit, a year or so ago, and I don't get the appeal. I like ordinary fantasy football way better, maybe because I do it with people I know and that's part of the fun. Then again, I've played Fan Duel with people I know too and it's still not much fun, for me at least.
The marketing angle seems to be that you can make money doing it. But of course, for every dollar one person wins, another person loses, and also people lose even more because the company has to run itself and make money. The TV ads, about a guy spending $200 and ending up with $50,000, or whatever, are incredibly cheesy. I feel like I'm watching an ad for the Psychic Friends Network or maybe the state lottery.
If your goal is to make money then there are many better ways. If your goal is to have an interesting competition involving friends, and maybe have some wagering involved to make it more interesting, you run it yourself without much problem and you'd avoid having a middle man take 10%, or the government 35% in the case of a big win.
To each his own, but it's not for me.