I just noticed in the exchange shop, these cost only 1 crystal, and you can buy 4 at a time, and you can get assault ++.At the same time, it almost looks too good to be true, like theyre must be a catch or something, or they wouldn't sell them so cheap. I've got 8 crystals to at the moment and my fire and wind grids are weakish. should I buy 4 of each, or should I do FLB with those crystals?