I know about the Sonaki vitamin C filter. The other "big name" in shower chlorine removal that I know is Aquasana. I think they both work. I noticed some reduction in water pressure, but I got used to it, plus I use an adjustable shower head so I can get the feel of more water pressure by using a stronger setting.
You can buy chlorine test kits inexpensively at swimming pool supply stores if you want to play around with testing your shower filter. Some people like to use test kits to determine when to replace their shower filters.