Duel is extremely fun to play. It's one of those Free To Play games that gives you an option to buy in-app, but unlike most of those Duel is pretty F2P friendly. The grind and the rewards are satisfying and the gameplay actually strategic. It can be a little repetitive, and if you RNG game is not on point, frustrating. Stick to playing it for an hour or two at a time and change up your team and playing style to keep things fresh and it'll suck you in for hours.