Asking for a review and doing reviews in Crucible is a multi-step workflow. Also, there is no clear list of what's already reviewed and what's left for review. Overall the tool seems "heavy".

I'm sure Crucible works great in some teams. CodeBrag is designed more for smaller teams, which want to have tools be as simple as possible (while maintaining functionality, of course), and like a simple, streamlined process.

For example in Crucible you need to create reviews (select commits and assign a developer who will review them), in Codebrag commits to review simply appear on the "To Review" list. It depends on the context which tool is more suitable for your team.