It all depends how/where you mount them. They come with a protective sleeve which has a very tiny slit for the light to pass through. If the slit gets covered in dust it will trip the switch. All my switches are mounted in a way that dust can't settle on them. If a piece of debris flies through and trips it then I can just blow it off with air and hit resume. In the future I plan to make a vaccuum cleaner hose attachment to the spindle which will suck up debris while cutting so this won't be a problem for me going forward.
If you like create a single sided pcb layout in express pcb and upload the file I will etch you some boards free and ship
Just in case you still look here ounce in a while, you mention the magic word, "precision". If you or someone else knows the answer, I'd like to know how precise is precise for this kind of sensor? I'd like to know if the aperture of the sensor as an effect on precision? Does someone know how repeatable these thing are? Anyone thought of using this type of sensor for setting Z zero? Thanks, Yves