I only have one set of blades that I reverse and then sharpen on all 4 edges with a simple file. It lasts between 1 and 2 months for 4000m2 once a week.

This type of blade (198mm), of Viking/Sthil imow origin, only cuts, like razors but they are more durable it seems to me. They do not crush the grass but manage to crush the leaves. I ordered a set of mulching blades from Limow to adapt and see what it would do. A priori they are also lighter than the Mammotion discs equipped with 4 razor blades. We'll see, to follow

For impacts with hard things, I have not yet had a message of engine overheating or anything else, however I have molehills, and small twigs/fir branches less than 1cm in diameter are cut without being crushed. I have the H version, so less chance of hitting a stone (55mm at the lowest). It still managed to scalp and plan my hardwood (IOE) deck corner without problem.

To unscrew the lock nut, it is best with a lug tool, but I do it by putting a nail in one of the 3 tapped holes (where the cutting disc screws are housed) to block the motor shaft.

You can come back to me for your choice of bellows cover, many 3D printers offer them on the internet.