Stack-on cabinet a friend was using at a worksite that was hit by smash and grab thieves one night. The cabinet was fortunately empty at the time except for a couple of packages of screws, my friend had been using it to lock up power tools, it was thrown around, jumped on, and had chisels and prybars used in the attempt to open it.
My opinion on them is basically that while they'll keep out some thieves, like in this case, that wouldn't of tried to carry out the cabinet, that's about all it will stop. Also if you're going to use one, understand that unless you bolt that sucker down to where there is no chance it'll be moved, don't put anything breakable in there. Judging by the damage done, any scopes in there would have been destroyed and a good chance that multiple firearms would mean at least some chipped crowns, among other damage.