For those of you who aren't familiar with string benders, they are a mechanism used to raise the pitch of a string, generally for steel guitar effects in the country music style, although they are as useful as your imagination and chops allow them to be. They are almost exclusively installed in telecasters (although there are some exceptions.)
I had a b-bender (string bender on the b string) installed in my telecaster by Charlie McVay, and I believe it is the best bender on the market. I have played Parson's as well as Glasers, and McVay's are unmatched in quality. Smooth bends, absolutely no loss in sustain or tone, and incredibly accurate. They also don't leave an ugly metal or plexi-glass plate on the back of your prized guitar like some do. Also, Charlie removes a minimal amount of wood during installation (about the mass of two 9v batteries.) He guarantees his benders for life, and the customer service is outstanding.
The bender is activated by a lever on the back of the neckplate, which you hook your strap onto via a Dunlop-style straplock. The advantage of this (rather than the Parson's which hooks on the standard strap button) is that you can bypass it if you wish. You still have your standard strap button to hook onto for non-bender playing.
I recommend anyone looking to have a bender installed to seriously consider a McVay unit. Brad Paisely would agree with me on this one. He owns a lot more of them than I do.