Oh, to answer the O/P's question about testing the output.
First: MSW is by definition NOT CLEAN.. But
There is really only one way to test it,, A very high quality 'Scope.. This is a tool an electronics lab should have and a technician may have.
But I do not think it is how clean it is,, I think it is the MSW waveform that bothers some hardware... It fools timers.. Certain types of voltage dividers work differnetly and several other things get messed up because instead of 60 cycles there are 120 or 180 or 240 steps per second.
There is a device I used on the farm to cross a fence.. It is a pair of steps back to back so you climb up one side and down the other.. Fence is in the middle. The animals inside the pen can not climb the steps so they do not get out.
Well it is called a STILE
And another thing that carries the same name is a pile of horse dung
And those steps look exactly like a MSW inverter's output
And you can draw any inference you like from that.
For more info on everything I just said save for the waveform itself google: Citizen Blue. And read the stories that are "Hits".