Security cabinets, Residential Security Containers, and bonafide "Safes" are all just tools to buy you some time. How much time you buy depends entirely on the type of security container you buy, the sophistication of the burglar, and the types of tools that they either bring with them or have on hand at your house.
Many threads of this sort eventually go in the direction of reminding people that residential security containers are not legitimate safes, and I suppose that's a true point from a burglary insurance standpoint. I can tell you that I've looked at getting a TL-15, TL-30, or TL-30x6 safe to keep my long gun collection safe (those safes are true, rated "safes"). The cost of acquiring such a safe is enormous in most cases, and they literally way 1-3 tons. I'd love to have a safe like that, but I haven't been able to justify the purchase in any reasonable way. But, the TL rated safes are the ones that provide you with true security against anything short of a professional safe cracker who has significant time and the correct tools to work on the safe.
The other extreme is the "stack on" style security cabinets. It's basically a glorified locker. If you have a pry bar you can open one of these pretty easily. Heck, you could probably open one with a thick screwdriver and a hammer if you were motivated. They'll stop your kids from getting the guns, and they'll stop the crackhead who quickly runs through your home with no tools, time, or means to transport the cabinet. These are low-security options, but they're better than keeping the guns laying on the kitchen table.
The intermediate option is a RSC. These are what you see at Walmart, Costco, Cabelas, gun stores, etc. The cost and quality vary greatly, but as a general rule the manufacturers overstate the true security of these safes. I'm not a safe cracker or a locksmith, and I'm confident that I could get into the high-end Liberty "safes" in 10 minutes or less using the tools I keep in the bed of my truck at all times (despite any of their advertising to the contrary). When bolted down these RSC will generally still stop most crooks even with crowbars and whatnot, but they're not going to stop someone who has the tools and time, and goes to your house knowing what they're trying to accomplish. Nevertheless, safes of this variety often represent the practical limit for what the average homeowner is going to be able to acquire (500-1,200 pound range in most case). They'll keep most bad guys out under most circumstances, but in my opinion they won't hold up against an attack by someone who goes into the crime knowing that they're going to try to crack a safe.
So, when people ask whether "x safe" or "y safe" is a good safe, I think it's important that we're all on the same page regarding what we're talking about. If you want a nearly impenetrable fortress of a safe that will stop even most skilled and planned attacks, then you can fork out the $7,000-10,000+ for a good TL30X6 safe, then pay a few thousand dollars to have that 4,000 pound object moved into your house, and then back that safe up with a quality alarm system. For the rest of us (like me), the chosen "safes" are always going to be a compromise, and it's hard to say whether it's good or not (depending on the threat you believe you're facing).
