I will never ever pay for a box with no way to see exactly whats inside first. Its one thing to have a mystery box at the end of an OP in addition to what you get normally. But to pay cash of my credit card for it? NO WAY in heck.
Be careful what you ask for, they'll end up putting a one-use only, stackable item on the cash shop that'll let you see what's inside a lockbox, for a fee.