Pay to play simple. If you want to play for free them expect your progress to take years (yes years)as rewards are next to nothing for completed quests. Ignore people who say they became uncollected with 4 star champs (easily) as the mechanism of the game has been changed alot since then and you will not be able to become uncollected unless you pay or save up 1000s of units(which takes ages as they drip feed you them) to buy revives and health potions.