I skid about 50 days last year, so I get a fair amount of use out of my rack. I've also seen a few different ones riding up with friends. Yes, a roof rack is nothing fancy, basically it just needs to work. Thule's does a pretty good job at this, I've had it get stuck once (freezing). I've had about 5 other racks do this too, and it seems pretty unavoidable, I don't leave skis on it at night, just to drive up to the snow, and back to the cabin. Its got locks, which I use more to ensure they don't come open when driving (I've seen unlocked racks come open, fortunately not both front and back at once though). A determined theif could easily get past the lock though, so I wouldn't trust leaving them in a high risk area - the racks just plastic.
As can be expected, it WON'T fit 6 pairs of powder skis, 5 skis is far more comfotable, although I've seen 7 on a friend's rack, all were narrow skis though. Also, if your roof rack's narrow (length-wise) and you have raceplates on your skis, you may have difficulty, although again this complaint isn't specific to this rack.
Honestly, I'd recommend getting the cheapest rack you can find of good quality (that feels sturdy). Ski racks aren't rocket science, and unless you really want one which slides out sideways from the car, any will work fine.