I have the basic set that use carbide tips, bought from Adendorf ( South Africa). They have 5 basic tools for left and right, a parting tool and a thread tool.
These tools work excellent on brass and aluminum, but it is another story on steel or stainless. The inserts are prone to chip, unless you take the smallest of cuts, I mean micro size. This have left a bad taste for carbide tips.
There is nothing wrong with the tool holders. They are 10 mm size (just bigger than 3/8). All of them is flat mounted. What I mean by that is that the tips are not mounted at an angle but flat. This same set is available in bigger size tool holders as well, but with the same tool inserts.
I rather use HSS tools and carbide tipped brazed on tools that I have to sharpen every now and then. Carbide tipped tools (home made with concrete drill bit tips that I have salvaged and brazed on my own shafts work the best and cost almost nothing).
I have changed my mind when since the day before yesterday, I have modified a QCTP to fit on my lathe and I just had to take of some metal from the bottom of the oversize tool holders. I have taken them to Steelcraft, my cousins' factory and used their Quantum lathe, as their milling machine was being used at that moment.
My cousin set the hardened tool holders in the chuck and he used a 20mm tool holder with a larger tool insert than my small ones. His have cutting edges on top as well as on the bottom (the tip can be turned over once all three corners are damaged). This tool changed my opinion again as this tool was able to cut better than I am used to with HSS and even with hardened steel. I am aware that his lathe has more torque but I did not take much bigger cuts than I am used to. I must also state that he use no new tips on this loose manual operated lathe. He uses the tips first for some time on his CNC machines and then take them over to the manual one.
This tool holder of him cost about R700.00 (about $ 120.00) and the tips about ($10.00 - $15.00). The set that I have was R945.00 (about $160.00) and they chip for nothing. I now use them solely on the softer metals like brass and Aluminum.