You cannot control what the contents of the box contains most of the time. It is just a big cash grab. I do play mobile games but I don't pay money for things I don't need. Also the biggest reason I don't by them is because they are not REAL!
Ah, Yes, The one reason I don't play any mobile game anymore. They basically work by giving you a fucking useless box. Butt wait, You're told that there's "a chance" tat you could get something incredible and legendary! So what do they want you to do? Sink your money into a whole bunch of keys to open them all up. And what do you get? A lot of slightly-better items and normal items. Oh yeah, Did I mention this is for one single day? LOOK, MONEY-OBSESSED DEVS, THIS IS NOT GAME DESIGN. THIS IS A FUCKING CASH GRAB AND WE ALL FUCKING KNOW IT. STOP.