Hi Capt,n
Boy "how smooth" is a leading question on a single cylinder chainsaw conversion! The two with electronic ignition are actually very smooth at idle and high speed with a little roughness going through the 3000 - 4000rpm transition. The ones on mag are a little rough all the way up to about 5000.
I would say they are smoother than a Quadra 42 - rougher than a Quadra 400 or a G45. Sorry I don't see many of the higher end motors in our club to compare with.
We have definitely had better luck buying new saws - some of the "reconditioned" ones are well worn and lacking in compression. Best is the "Pro" model with chrome cylinder. It has a slightly larger carb and better bearings.

Dave