I've had my Aerostitch for a full year now and wear it commuting every day. I finally, just a month ago or so, got the hip pads and back protector. Before that I would wear a separate turtle-shell-style back protector; but that was just another piece of equipment I had to put on every morning and evening.
There are two back protector options available, as shown on this link: I got the $60 model.
Suit Accessories
The back protector I bought is a very rigid, thick rubber(?), and it certainly looks like it'll do the trick in the event of an accident. Along with the hip protectors, which seem to hinder access to your pants pockets (not a big deal for me), the back protector does tighten up the suit, making the zipper a little snugger closing, particularly in the winter when wearing a 'lectric vest and sweatshirt. Photo of installation, below.
The biggest issue I had with the back protector, which I believe I've solved, is that I had to adjust its positioning up or down the spine of the suit (using the factory velcro tabs) so that it would not rise too far up the base of my neck and give the a feeling of restriction in tilting my head--I felt like my head was being pinned forward. I'm not even positive the protector caused that feeling. I think it might have been principally caused by the thick stand-up collar on the Aerostitch. I finally just got a huge safety pin and pinned the collar all the way back off my neck (photo).
Also see this recent thread:
Aerostitch Thread As note there, I am very pleased with my 'Stitch, including the hip and back protectors. Two thumbs up.
Jb