the 266 is for fluidline or cream liners and some people like to use it to fill in their brows. here's a video review of the 219 and 239 brushes. it's a guy but the video is really detailed and helpful :).
http://youtube.com/watch?v=ONqU8t7HiJM, 219 brush.
http://youtube.com/watch?v=dZzKIfU3X9w, 239 brush.