I just used the BeautyBlender BlenderCleanser (LOL!) from my Birchbox for my makeup brushes. The cleanser itself did pretty well at cleaning away all the makeup and dirt that had accumulated on my brushes. Really quickly too and not too much "scrubbing" to get it to lather to cleanse.
I'll go ahead and edit this post after my brushes dry to see if it will affect my brushes, post washing.
One complaint I have so far is that the smell is really strong. There is a lavender scent to the cleanser and its really strong. Like a bad kind of strong. It's less floral smelling than you'd think and more of a chemical type of smell.
I went to check on my brushes after 2 days and they seem really clean and soft. It seems there is a slight residue left on the bristles. Like a greasy or waxy kind of feel when i went to touch the bristles, but i cant really say it was from the prodct. It could have been from a less than perfect rinse out. The next time i wash the brushes i'll use up the rest of the bottle and see if it was my mistake or actually from the cleanser itself.