You know, I could go on and on about this. So get ready. :cool01:

ccasion14:
I'll divide the discussion about history, construction, ease of installation, and playability. I have 4 bender telecasters now, so this is all from personal experience and not third hand knowledge.
History:
Parsons/White. This is the first bender created. It was a joint collaboration between Byrds guitarist Clarence White and sometime Byrds drummer Gene Parsons. Clarence wanted some kind of device to pull one or more strings, and Gene had access to a machine shop. Some work later, the result was this:
The bender mechanism was 'borrowed' from a pedal steel, other parts were made from scratch, and the whole mess was bolted to the back of the guitar. Gene made the guitar's body thicker by screwing a telecaster shaped wooden 'spacer' thingy on the back. Clarence was a bluegrass flatpicker, so he didn't mind the extra body thickness. He also didn't care what it looked like apparently.
Other folks heard the guitar and wanted one. However, they were not keen on the hacked up nature of the above creation, so Gene got his designer hat on and figured out how to embed the mechanism inside the guitar body. The result is the classic Parsons/white bender:
Much neater than the original guitar, but still a pile of work involved to correctly route the holes required. In particular, the hole needed to hold the pivot point near the bass bout needs to be precisely machined or it will, well, fall out. Then there's the holes for the bend pitch tuning (on the top) and the hole where the arm extends out the front of the body. it all adds up to loads and loads of fine wood machining to get everything to work right.
This was not so great for mass production.
Anyway, Gene was happily making these custom ones for guys like Pete Townsend and that guy from Led Zep (who was that again?) when fender showed up. I was not there, but I imagine the conversation went something like:
Fender guy: "Hey - we really like this thing. We want to license it and put it into our guitars"
Gene parsons: "groovy man"
Fender guy: "so - what do the parts cost?"
Gene: "well, about XXX"
Fender guy: "!!!!! er, wow - that's a lot. Well, what kind of labour is involved in doing it?"
Gene: "well, the last one I did took about YYY"
Fender guy (Grabbing his chest) "Holy Crap! that's insane!"
Gene: "yea man, it's pretty groovy."
sometime around this point, a women named Meridian Green showed up <Edit - I got her name wrong. just fixed>. Somehow, and again I was not around, she talked Gene into building a cheaper version that was even cheaper to install. Then she talked fender into licensing that.
This was the classic Parsons/Green bender:
Here, all of the mechanism is attached to a steel plate and installed as one unit. The installer just has to route out a hole in the back of the guitar and bolt the plate to the back to the guitar. The hole did not require machinist accuracy, and the entire unit was dramatically cheaper to install.
Next installment: construction and ease of installation!