I find it very satisfying when making something simpler also makes it better. I tested the simplified heater / nozzle design using the same stainless steel insulator and heatsink arrangement, so I could get a direct comparison of the results.
The heater warms up a lot faster than the one made with two AL clad resistors. It also extrudes faster and the times are more consistent. ABS pushed with 2.32Kg went from 3.7 mm3 to 4.6 mm3, an increase of 24%. HDPE pushed with 4.6Kg went from 3.8 mm3 to 9.3 mm3!
The nozzle is 0.6mm rather than 0.5mm, which reduces its contribution to the pressure by a factor of 2, but all my other tests have shown that what happens at the other end of the heater dominates the force requirement. As I improve things though, the nozzle hole becomes more significant.
Here are the drawings :-
Although it looks complex it isn't difficult to make with a drill press, drill vice, and some taps and dies.
I glued the thermistor in with Cerastil, but I expect it could just be wrapped in tin foil and jammed in like the ceramic resistor, taking care to insulate the wires of course. I use PTFE sleeving.
I didn't need to seal the threads with PTFE tape. I just screwed them up tight and there was no sign of any leakage.
The next thing to try is putting a taper in my PEEK version to see if that can be made to perform as well as this one.
Of course I haven't built anything yet with any of these designs, so caveat emptor.