My vote goes to being able to cheat but only if you actually plan on highlighting the fact that the MC is cheating. He should feel guilty about it or worried about the girls finding out about each other, depending on his personality (maybe he's not sure which girl he prefers or he's just a playboy type).
If the game never acknowledges the fact that he's cheating and he never thinks about it, you might as well just make it a harem from the start. And to be honest, that's the option that will likely get you the most players/patreons. I've seen a fair amount of users on this forum that refuse to play anything but harem games, either because they don't want to do multiple playthroughs or they feel bad for the girls that get rejected.