Ooh I need to make some flash bangs soon, and yours look so nice and clean. Great looking work man, your peps are super clean.
With bondo though, use as little as possible, and while it's curing use a razor blade to cut the high spiky crap down. It's worth investing in a hand plane, a rasp and a file too- and the final secret ingredient is bondo spot putty (sometimes called glazing putty).
When I'm doing a bondo job I lay down a layer, use the razor blade to make sure everything is almost level once the bondo gets rubbery, then I use my rasp to take everything down to level when it gets a little closer to cured. Next I take my file and further refine and shape the spot I'm doing (work in spots rather than whole areas of a piece). Then 80 grit sandpaper. If I have excessive low points or pitting I'll mix a small batch of bondo specifically for those areas and do the whole process again, but just on a smaller scale.
Once all the big craters are filled I use a credit card to smoothly apply spot putty to the whole bondoed area and then move upwards in sandpaper grit from 220-400 and onwards.
i hope I have given some useful advice, rather than unwanted advice on that- my first my vi helmet and chest had bondo that looked just like your helmets on it, so you're at least on the right track for a first timer with the pink goop.
Keep eps it up man, I love odst builds.