With the big Berg, didn't have many issues. Changed the starter clutch after 3 seasons - that was a manufacturing defect most likely. And needed new piston rings and valve seals at 150 hours.
The little chipmunk went through two spark plugs during break-in until I figured out it was set too rich from factory. I adjusted it to be leaner. You have to be mechanically inclined on the two strokes, especially if you buy new, since they are quite particular and weather-dependent.
Not a huge deal though. Changing the jets inside the carburator is weird to have to do, but not more than a 30 minute job.
In terms of regular maintenance, changing the entire top end at 50 hours costs about the same as just checking the valves on a four stroke and you never have to just check the valves :). While I never checked the valves myself, I already changed a pitson on a small 50 of my son's, a few years back. It's easy: you do it yourself, in the garage - it's that simple.
My son's two strokes (a 50, 65, 85) never really needed any maintenance, other than some blown clutches on the 65. The 50 sucked some dirt once and I needed a new piston - did it myself for 100$. While on the four stroke, you feel it always floating in the air: the danger of big expensive damage to the top end.
Missing the starter button, for sure. You sometimes stall it in the weirdest of positions, where I can't reach the kick start and it gets hairy. I am getting used to that and I seem to stall it much less now - you get used to riding the clutch. It is tall though and reaching the kick-start is an issue sometimes.
I was shifting it a lot in the beginning - I don't know if I am shifting more than I did the 390, which I short-shifted most of the time. I am shifting it a lot less now that I got used to the power-band and the clutch.
Continue to part 3: differences in riding technique and conclusion: KTM 150 XC vs Husaberg FE 390 Riding.