It's got a one round delay from when you start using it until it actually triggers, so it's less than perfectly useful in an encounter. You'd usually only want to use it out of combat, barring emergencies.
The box is way cheaper than any other spell storing option. The only other one in its price range I could find was the cracked Vibrant Purple Prism ioun stone, which is 2000 gp for only 1 spell level stored.
It's not a good trap, though. The spell is a touch spell, but disarming it is as easy as starting the solve, then putting it down and backing up a bit during the one round of pause in your solve attempt. The spell discharges, doing nothing to you because you aren't touching it, and then you can pick it back up and solve it in the remaining 8 rounds or at your leisure the following day with no more spells stored inside.
The spell automatically hits any creature holding the box. Does it hit all creatures holding the box? Does this let you share touch spells across more recipients than they would normally allow?