I do like the muffler, it makes the engines very quiet and it keeps the oil away from the plane. But the muffler does make starting more difficult as one cannot simply prime the side of the piston. I guess one could easily add muffler primer tube, but I haven't tried that on PAW.

It is very easy to overprime the engines when priming through the carb as the crankcase tends fill up before you get fuel to the top on an upright mounted engine. Side mounted are easier, or simply hold the plane rotated 90° and turn the engine over, this way the fuel will reach the top (above the piston) more easily and there is less risk of overpriming. Turning by hand you will feel when the prime reaches the top and it is time to flip it for starting, or if you have over primed and need to empty that first.