Think you mean 'SOOT" not suet. Suet is what birds eat........
Every stove I've ever seen dirty the view glass, it's a matter of life and so is cleaning it (if you like seeing the flame, in my case it's not all that critical.
Like I said, the all do that, especially on lower settings because they don't get internally hot enough to burn off the soot and change it from black to light grey which you can see through. Crank it up a bit to keep the view glass transparent, well, not black but light grey because it will still get fly ash on it.
I like to keep a paint brush with natural bristles handy (don't use a ploy bristle brush, it will melt to the view glass and that ain't good.... Open the door while the stove is running and brush off the glass with the paint brush and call it good for a day or so.
You MUST run ANY stove in the higher ranges to keep the view glass somewhat transparent. LOW settings will always blacken the glass, don't matter what brand of unit it is.
The manufacturers 'air wash' is just that. Hot air and no wash.
I do 75-25 myself. The pellets keep the corn clinkers under control.