Re. sanding and shaping, in my experience aluminum-bearing fillers are a bit tougher to work than Bondo, but not enough to pose a problem. I start shaping with a body file, then work down to 320 grit. If I find small pits I use spot putty, and also use it to hide minor edge lines that show up after priming. That's something I always wind up having to do, being among the world's worst at paint-and-body work; takes me a couple of weeks to do what a good hand can do in a day, but the results hold up long term.
I’m intrigued by metal body filler. What are the benefits over the ‘bondo’ stuff?