Should I reroll in brown dust?

Rerolling will give you a chance for better heroes but will erase all your progress so far.

If you haven't made much progress yet and you are not happy with the heroes you have then its worth doing. But if you are already some way into the game you will have to start again.

I spent about 7 hours rerolling but was worth it. Got 2 5 stars I wanted (browndust was only offering one guaranteed 5 star at the time of rolling) definitely worth it in my opinion