I have heard of it. I will give it a try. I just never got around to using it because bondo is so readily available. Bondo also works good with you mix it with resin. I like to use that to get a thick self-leveling layer that is extremely smooth.
Looks awesome! I do a make a lot of molds for fiberglass. I use bondo for the final layer to be smoothed. It feels in all the imperfections, it's hard, sands very good, and paint/epoxy sticks to it really good.