I'd stick with a regular old pulling comb, and ignore the gimicks of these new ones. http://www.smartpakequine.com/aluminum-pulling-comb-208p.aspx?cm_vc=Search
As far as how they work, brush out the mane, taking small sections at a time (I prefer half inch or a little over), tease the excess back, wrap it around the comb, and in one quick pull, you have your mane. Brush the teased part out, and grab the next section.
My horse has no problem with pulling, and just stands there asleap, but some are more sensitive and will fuss. It's best if you pull in small, spread out sessions, and do it after your horse has been excercised. When they're warmer, the pores open up, making it easier to pull.