The hotend of the Vertex Nano K8600 is much better than of the Vertex K8400. Shortly I bought the K8400 two years ago, I changed the original hotend against a Mendel Prusa.
But even the better hotend of the K8600 should be improved.
First, the fix wiring of the nano should be changed. It is impossible that the hotend never gets problems with Filament blockading the “heatsink”. So the hotend has to be dismantled. With a plug which connects/disconnects the hotend, the temperature sensor and the fan, this task would be much more easier. I will do it in any case.
Second, the heater block is not well constructed. It is just a Aluminium block in which a Drilling was cutted alongside, so the heater cartridge has to be clamped to fix it in the heater block. But the aluminium block bends, so an once old heater cartridge will be difficult to get out. So you have to use a flat screw driver to widen the slot to get the cartridge out again.
A better construction would be a normal Drilling, maybe 0,1mm wider in diameter than the cartridge. Fixed in the drilling should the cartridge with an M3 setscrew. Same thing with the temperature sensor. Not from below. Better from the sides.