I much prefer trans-mapped brows over brows that are part of the face texture because they are so important in the look of a character. One little change often changes the whole look of a character. I actually went through all my runtimes and made folders and mat poses just for trans-mapped brows for whatever characters I had where it was an option, so that I could easily change the brows to suit what look I wanted. I've also photoshopped the brows out on favourite textures so I could use trans maps on their brows.