In reality, unless you are installing in a poured concrete wall, the vault door will be a serious waste of money. A steel door and multiple decent dead bolts, maybe a double bar fox lock will be 1/10 the price and offer just as much security as a vault door in a standard construction wall. It will also attract less attention to someone ransacking your house. In any vault, the walls, floor and ceiling are faster to breach than the door itself, but putting one in wood framed wall is pointless and a waste of money.
Remember, they dont have to make a 4'x4' hole, just one large enough to squeez in and pass out your guns. 16" on center studs with even double thick sheetrock or old school plaster can be smashed through by kicking it in less than a minute. With an axe or some type of prybar its about 15-30 seconds.