Like all good tools they are not without there learning curve.
It is not just a matter running them on a messed up fender. You can make a messed up fender well beyond repair with improper use. In fact, I would likely pay more for an untouched damaged fender then one that someone tried to repair.
Other tools that give similar results are the air hammer frame variants such as:
Watervliet
There is a Harbor Freight variety too.
I have the Watervliet (and a few others) and tried it on a fender that must have been driven with loose snow chains. It was a pitted rear fender and it made a good test case. With a bit of experience I can see how these tools can work wonders. I also know they can just as easily ruin a fender's shape.
Then there is the time tested and slow hammer and dolly techniques. Augmented with a shrinking disk and you have decent results.
The powered tools and the hand wheels are trouble because they can over work the metal too fast. They can quickly stretch the metal and on some curves this can be the kiss of death to all the but the best and experienced metal workers. I had to fight this problem with a fender I had and is the reason why I would rather fix a nasty bent up fender over correcting bad metal work. I had to compromise and have a shape I did not like, but I just could not get it exactly right after a lot of work.
My take, If you are just doing one car. Learn the metal work (see my tech tidbits on metal work), get some high quality body hammers and dollies, and get a shrinking disk set up. Pretty low cost and a lot of bang for the buck. Plus you will still use them if you go more advanced.
The most important tool in body work is a well educated brain.
You have to be good at solving some puzzles.