I think that is the unit I bought at Wal-Mart a few months ago for about $40; grey in color, with a strange four-sided key. It's definitely a Sentry and the size sounds right. I bolted it solidly to a bureau and use it for securing carry guns when I don't want to open and close the big safe downstairs all the time. It's a lot better unit that the ones in use in many jails and prisons--which is a little scary...
I thought it was a pretty heavy duty unit for the money. Someone would have to work pretty darned hard to get it open. If I expect to be gone overnight or for any length of time the guns go in the big safe, though.
I would recommend it if you don't mind having to use a key everytime.
