QCTP are useful time savers, if only from the aspect of not needing to shim the tool to centre height when you come to use it . But space is needed to store the holders not in use.
Without a QCTP the shims needed for any tool can be held with the tool by gluing in place or merely holding with an elastic band.
Some time ago an article in MEW extolled QCTPs but said that changing tools could be no quicker than unlocking and rotating a four way toolpost!
Having a small shop, the space for storing spare QCTP holders is lacking, so I survive with front and rear four way toolposts,. These allow the use of six tools,(Rough turning/facing, Finish turning/facing, Boring, Front chamfer, Back chamfer and Part off ) without any changes being required, so tool changes are only needed for Knurling, Screwcutting or Radius turning.
Unfortunately, not all Top Slides have the facility to mount a rear toolpost.
If the space were available, out of idleness, I would probably change to a QCTP. They were devised for Industry where time is of the essence
Patience has never been one of my traits, but being retired, time, for most jobs, no longer presses, so the 4 ways suffice..
Hopefully this presents both sides of the argument.
You makes your choice and pays your money!
Howard