hmmmm, I asked myself exactly the same question about a year ago, my thought process went something like....
1 I need a new QCTP to eliminate tool overhang and chatter on my Sieg C3
2 I can afford the cheaper ones, but I have a cheaper one on the machine and it chatters, and "Machinery Design 101" says that the three major requirements of a machine tool are, rigidity, rigidity, rigidity. So steel only.
3 Can't afford the steel ones, which are very nice from LMS etc, freight alone was too much!!
4 Design my own, quickly eliminated those types with features that were beyond my capabilities (actual or planned!!) and I ended up with a post and clamp on type.
5 Have a look at
http://madmodder.net/index.php?topic=3823.0 where there are some photos etc
I've used the new toolpost a fair bit in the last six months, and can fairly honestly say that the only criticisms I have are that the two cap head screw toolholder clamping is a bit of a bore, but it is VERY secure, and changing toolholders is not quite as quick as with the old system, but then I'm definitely NOT in a production environment
cheers
Bill Pudney