As I understand it, sword canes are illegal to carry around just about anywhere. I don't know whether they are allowed with a CCW, I think probably not because you aren't concealing the weapon, but the fact that it's a weapon.
Ignoring their legality, the cheap sword canes are useless. They have low quality blades that would be far less effective than a simple cane/club. And since the cane is hollowed out to accomodate the 'sword', it is probably too weak to make an effective club. Also, the cheap sword canse have to be unscrewed, which takes several seconds, and alerts your attacker that you have something hidden in the cane.
The good sword canes have full length 'epee' type blades. These are triangular blades with little or no edge. Kindof like a really big ice pick. Also, the good canes are typically a bit sturdier and the cane can be retained in the offhand as an effective parrying/clubbing device. Also, the handle and sword are easily and quickly released.
But again, if you don't know how to use the 'sword', you are probably better off using the whole thing as a club.
It is very important for you to realize that a sword cane is almost useless as a slashing weapon, even the ones that have an edge. The blade is simply too light, and too long for you to get enough leverage to inflict more than a minor cut. If you can't stab the bad guy with it, you can't hurt him.
I am one of the senior members of my universities fencing team, and I specialize in epee (which is supposed to emulate a duel). While this by no means makes me an expert in the use of a sword for defensive purposes, it does make it's limitations painfully obvious, especially when watching how the newbies try to wield them. Most of their attacks flat out miss thier opponents, they simply haven't developed the necessary point control to make their blade go where they want it to, especially when there is some sort of contact or defensive action involved. If you are fighting someone with a knife and you miss, you are at their mercy because your point will be behind them, and they can gut you at their leisure. Unless you really know what you are doing, infighting with a sword is almost impossible.
Unless you are skilled enough with your sword cane to stab the bad guy in the wrist without getting close enough for him to swipe at your arm, you probably shouldn't bother with one because you will be forced to get close enough to stab him in the body, and he will take out your arm.
I typed this fairly quickly, so I will probably have to edit and clarify a few things. Bear in mind that this is coming from a fencer's standpoint, not a truly practical one. In real life you could kick, etc, and I am used to fencing against people who are armed and trained in a similar fashion to me.