That cabinet has all the requirements that I would look for in a handgun cabinet; ample space, very well designed, locking (kind of obvious), a very classy look (so it wouldn't be sequestered to the basement, garage, or utility room), and concealed (anyone who sees it just thinks it's a cabinet of some kind, but most would not suspect that it holds a small arsenal of pistols).
All-in-all, very well done, you and your father should be proud of the design and of the craftsmanship that went into it.
I have a mild interest in guns. Actually, I think the clinical term is "obsession," but that makes me sound like some kind of gun-nut. Which is fair, since I am.
Wastin' away my future children's inheritance one box of ammo, range fee, and bottle of Hoppe's #9 at a time.