They work every time for me... never (in 100's of tire changes) have I had one loose nut.
I have seen torque sticks that don't work.... only when you are running low on air pressure and the impact is not hammering properly or if the torque stick had been abused.
The torque stick is just a piece of spring steel designed to flex at a specific torque... If using an impact on a springy object capable of absorbing energy, the impulse (hammering) will simply be absorbed, and virtually no torque will ever be applied. The torque stick acts like an extension till the designed torque is reached, then it becomes springy.
Note: They can drift if misused (just like a torque wrench)! DO NOT USE A TORQUE STICK AS AN EXTENSION!
Another note: they can produce +5 ft/lbs over spec at extremely cold temperatures (below freezing).
Sorry for all the rambling.... but I feel they have a bad name due to misuse and lack of available knowledge. I too used to think they were just a gimmick, but after reading up on them and experimenting a lot, they have a permanent home in my toolbox!