The card gachapon can be cruel but in they have big events that let you do lots of draws for free.
The main story is gated, which you need to pass by leveling up your cards. These "battles" are a bit annoying. That being said, I love the story and had to put N/A for value because I'm a whale in this game. Mammon can yell at me from across the room all he wants. I'll tap Diavolo until he stops looking sad. Make_Satan_meow.
The writers did a good job with demon lore. It's all hidden behind this goofy veneer, but there are little details I am surprised they added (like Mammon's connection to England). That makes the story even more fun to read.
If you need 7 to 14 more loveable idiots to love, look no further.
The characters are "brothers" in the sense that they were all angels created by god. Beelzebub and his "twin" were created the same day, but Beelzebub explains in game that they aren't actually twins. They refer to each other this way because they share a birthday.
It's a bit odd they refer to each other as brothers, but if you play the game, they explain they are not actually related, simply close because of their collective hijinks through the aeons. I provide this explanation for anyone who may have seen reviews mentioning sibling stuff.