Egerandi and Trainer, sorry but I can't help you with the comparison to either boom or tawny as I don't own either one. Hopefully someone has all three and can help you with this. Prehaps Jen could swatch all 3 so that it would be possible to see the difference.
Trainer, in answer to you base question, I use it much like Egerandi, but I also have used it as a neutral shade under shadows to build additional colors on. Yes, I do use a primer most days ( Karen's), but part of the fun with eye shadows is just playing with them and combining , layer, etc in different ways to see what looks and combinations are uniquely yours and that you love.