I don't see it being terribly good as is. It's a good idea with some drawbacks.
1. One of the first places a thief toss's is the bedroom and the bed.
2. As another poster pointed out, that is a lot of weight on four legs.
3. Access is cumbersome, so it only practical for long term storage.
Long term storage in a guest bedroom would be the best situation as is.
But it would be really great idea for a in the floor long term storage safe. If you were building a new house you could make room for it in your foundation. Then hide it with a desk on rollers perhaps.