The following video shows a Z wave light switch that doesn’t require a neutral (the GE switch in the video has been discontinued, but Cooper still makes one) tested with four different kinds of bulbs:
A conventional incandescent,
A conventional CFL,
A dimmable CFL,
And a white only dumb LED bulb
They didn’t test a smart LED.
Even in this very simple test, you can see the flickering problems with the CFL bulbs.
The plain white LED actually works pretty well, although not as well as the incandescent.
I still think it’s best to use a neutral wire, but it is possible if you only have the two wires available and you get the right switch and the right fixture and the right bulb.
We should also note that sometimes you’ll only see flickers at full on or below 25%, but not in between. There are many people who only dim between 50% and 90%, so they might not see flickers while someone else who uses a wider range does. This is why sometimes only one person in a household will complain about flickers.