Not experienced with that particular tool, but I had a body shop pro with 30 years experience roll the rear fenders on my MS3. What did he use? A sledge hammer and a block of wood wrapped in a soft cloth. He held the block of wood wrapped in soft cloth on the outside of the fender lip to provide resistance, and gently tapped the inner lip with the sledge hammer. Back & forth several times, gradually bending the lip.
On one hand, I felt like a sucker for paying him to do this, because I probably could have done it in the driveway. On the other hand, if he screwed anything up, he'd fix it. If I tried & screwed it up, I'd be paying him to fix it.
Oh, and he didn't use a hair dryer or heat gun. We're in FL, so it was already warm outside when he did this last Summer, but used no additional heat source.
