The Hipshot Extenders are excellent, and the guys at the company are really dedicated to making a great product. Call and talk to them about exactly which model to get - there are many variations that they've developed to maximize compatibility and functionality.
Their manufacturing project is pretty complicated. They start with the OEM head that you have (Gotoh, Schaller, clockwise, counterclockwise, whatever). They actually disassemble it and lengthen the center shaft to accomodate the additional thickness of the detuning mechanism. They have different variations of the baseplate to fit different instruments as well, so you can put one on a 90 Fender Jazz and not have the baseplate hanging over the edge of the headstock.
The Manring Hyperbass is totally wild. He has an Extender on each of the four strings on his headstock so not only are there many alternate tunings, but he will flip pairs of them to get a pedal steel effect. But that's not all. He also has a special bass version of the Hipshot Trilogy guitar bridge. Each string has a lever on the bridge which can raise or lower each string to two alternate pitches. These alternate tunings don't have to be a half step or step up or down and the up and down transpositions don't have to be the same either. So there are a lot of possible tunings and different ways to get there. The bridge is not sold retail and you don't even get one on the Manring signature Zon Hyperbass.
I've watched Manring playing lots of this crazy stuff up close at the Zon booth at NAMM and I can't figure out how you even think about playing an instrument like that. He has certain pieces that are played in a more traditional style without too much transposition and other pieces where a lot of the playing is open alternate tunings with a lot of changes.
If Michael Manring boggles your mind, go see Adrian Legg sometime... His CDs (especially the earlier ones) are pretty amazing, but you really need to check him out live. That's when you realize that what you thought were three overdubbed guitar parts are actually all done by one man on one instrument at one time. His instruments have banjo tuners on all six strings, with an alternate tuning stop. He changes tuning while playing but often you can't tell that he's doing it (well, I can't). Just amazing. I saw him in a little soundroom at NAMM and we had the opportunity to ask questions during his set. When asked about his influences, he mentioned that his techniques derive from banjo and pedal steel as well as non-Western alternate tuning. Just doesn't sound like any of that stuff to me!
David Fung