23 cents, it looks like those blocks will work for very gentle shallow dents. Dents that will "pop" back into shape. However, for sharp dents, I can't see it working.

btw: there are techniques used in the tubing related industry that uses hydraulic pressure to pop dents out from the inside of hard to reach places. so maybe if you use a hydraulic pump and the blocks....

Also, there are other techniques to fill a tube w sand (or simular grain solid) or a liquid and then work it to shape to prevent kinking and other unwanted "dents". I think that some bike manufacturers are using these kind of techniques to shape tubes.