kong, i guess it depends a little on your use - if you are setting up production or looking for a turret lathe type set up that’s one thing, but in a manual situation the value comes from 1) the speed of the tool change 2) that the tool is preset in the cartridge at centre height and 3) the general rigidity of the set up. Whats the trade off? $$$$ and rigidity - even the best are less rigid than a blocked set up on the compound and the oldtimers will tell you to lose the QCTP for heavy, demanding jobs.
After having used a very expensive quick change tool post (
http://www.drehblitz.com/) with accurate indexing for many years (in a non production environment), I can tell you it is an amazing addition to the shop but the index-ability is of negligible value. Most of the time I make an analogue adjustment (loosed the bolt holding to the top slide and put the darn thing where I want it).
Therefore, if you study the Drehblitz site and discard the need for indexing you can replace the spline piece with a cylinder. That moves squarely into what we can make at home – it’s basically a cam-lock system. I can take some close up shots if it would help.
Mine came with the lathe but with only 1 cartridge. Fortunately, I didn’t have to make the turret but I’ve made a dozen cartridges. They are not hardened and ground but are more than adequate and I’ll never wear them out.
I’d recommend against using a rotary table as it does not address points 1 & 2 above and impairs 3, (all just imo, each builder has their own objectives). Radial motion of the tool is, imo, only necessary or desirable for radius turning. When this need arises there are easier ways to deal with it.