Very nice Mike. That gives me an idea for my collection of antique shotguns.
I have been wanting to make a display case for them but didn't want something that could easily be carted off. I could use this same principle but put my steel box into the wall first then cover it with veneer. Do the same with the door, use a steel frame covered with wood so it looks good. Use a high quality reinforced glass and I think they would be pretty safe.
Actually I traded some of my labor for a top-of-the-line set of clubs complete with a custom fitting. There was quite a bit more to the job than just the niche, I haven't been able to photograph it yet.