I also have some 18.5AWG Litz-wire, and I'm just now trying it out. Due to the mention of them for the Kairos kit in Meniscus' writeup, I figured it was due time. I used my jig as before, and wound up 7 layers, and came out to 0.436/0.428mH and 0.3 ohms DCR.
The finer strands in the Litz wire pulled a bit on the particle-board fibers, so I may have to invest in the slippery-plastic to make bobbins for my jig. This way they won't snag like they did, even though it was a minor movement and nothing broke as a result. Being these are the first pair I made of the Litz's, I think they turned out rather nicely.
Caveats of this wire format-
-The previously mentioned pulling of strands
-The wire is more flexible, and therefore the coil can be squished easier, and keeping the shape is indeed important. I would advise a poly-dip for this type of wire because of this issue.
-ability to check value is harder mid-winding, because the wires need to be soldered to be electrically bound.
-soldering is not as easy- I used a 100W gun to solder the ends of these together, another option is a solder-pot which can be extremely dangerous to those unfamiliar.
-tables that equate wire and size and number of turns are likely to be more effective at getting your approximate value before soldering the measuring to verify.
-zipties in my jig will bunch the wire more forcefully than with solid-core, so I used more zipties on the perimeter to make it more uniform.
Since I used the same bobbin to wind a value of another coil with solid-core, I counted the layers and went with that for these, and came out pretty close. So that is another way to approximate a value.