They seem kind of pointless, I mean they can only have items that weren't bid on, not just a random item from the BMAH. Odds of getting something worthless is really high, because any good item (rare mounts, good gear, etc.) will have sold for something. Even on low pop realms, if a rare mount shows up someone is definitely going to buy it, so there's really no way you'll ever get a mount out of the container. You could probably get gear sometimes, but even so odds are high it won't be gear for your class and it'll be BoP anyway. I really can't see buying these, even if you're basically at gold cap you could always find something more useful to buy.