Just so you know, I tried to bind it as ammo and it worked. But if you unbind a non-ammo slot, like your armour or weapon after you have the surgebox, the surgebox will count as both an ammo and armour/weapons slot. You cannot bind a new weapon/armour slot after you get this surgebox.
I don't see that being a big problem- they are dropped by celestial mages, from whom, even if it's a rare drop(~1/30), you are bound to get one per large dungeon.
I see the surgebox being much better in daemonheim than anywhere else, and the question now becomes- which is best, sagit(p++), laws or the surgebox? Not an easy choice, really.
Also, how much mage attack bonus would you need to not miss too much on forgotten warriors- the surgebox+hood are +13, with sagit body/prim chain it's -2, -17 with prim plate...