All mechanical, no batteries to die and fail on you. Also, no easy way to open the safe from the outside (most of the gunvault/stack-on/etc safes can be opened without a key/combo in under a minute if you know what you're doing).
EDIT: I should say, I'm planning to get one soon. For now, I have this guy:
It's within arms reach of where I sleep. My gun's on my hip all the time, unless I'm sleeping or showering. Its in there when I'm sleeping. It works well enough for me for now, but I'm paranoid about the batteries failing and have been changing them every 2 months. Hence the reason I want to go to the Ft. Knox safe.