Myself and @jimandyen are intrigued to hear some feedback from other K1/K1 Max owners who have tested third-party hotend upgrades and what your experiences of them have been.
Creality have the new Revo style ceramic hotend and Micro-swiss have the Flowtech nozzle kits and would love to hear feedback from anyone who has had the chance to try them out, thanks 
That does look like a very cool hotend kit I have to say 
I have purchased and installed the Micro Swiss hot end on my K1 Max.
I love it. The .4mm nozzle, that is. Printed a benchy after the changeover and it looks great.
Just today I swapped out the Micro Swiss .4mm nozzle for a .6mm that I ordered from them later. It’s a big print but the layers I see so far look pretty good.
I have to say though that installing the Micro Swiss hot end was a bit tricky… not their fault, though: their instructions are excellent and the hot end is very well engineered, indeed. It’s just that the wire connections to the existing hot end were glued together by Creality and were a bit tough to pull apart. So be careful not to bend or break the connectors.
Yes, I think once you install the Micro Swiss Flowtech hot end you can only use the Micro Swiss nozzles. That’s because the hot end, itself, is of specialized construction and the nozzle cylinder therefore needs a specific length and diameter. Already Micro Swiss has .4mm, .6mm, and 1.0mm brass nozzles available, and their sales manager informs me that they will soon offer steel nozzles in various sizes.
And now that I mention the 1.0mm nozzle I’m a bit puzzled why Creality Print does not include that size nozzle when adding a new K1 Max to the printer list?
When you swapped out to a .6 what changes did you set in the slicer…?
I use Creality Print for now…
They might not have a profile for that nozzle ready. Who knows…
In Creality Print, click on the Add printer button, then select the K1 Max, the program will ask you for a nozzle size, and then you’re all set. Your new printer will show up in your printer list as K1_Max_0.6 Nozzle, and one profile named “Normal” will include all the recommended settings.
I cannot say any good word on micro-swiss hotted. We installed it and afterwards the filament (silk from Reality) started to stuck in the extruder after every print 
