Which Type of Limit Switch

[EddyCurrent]

Maybe the mushroom reference is to do with the red botton on an E/Stop, typically referred to as a mushroom.
The one I bought was from a place that had closed and they were clearing out the stores.
You are correct about these not being applicable to hobby use but when you consider what's inside it can work out cheaper than standard relays, timers, etc.
Also I value my health so I'm prepared to go the extra mile to preserve it.

[Neale]

Mine was cheap because it's an obsolete model and therefore probably no longer certified for new build commercial equipment. Box was damaged as well but relay looks in perfect condition. What I haven't seen cheap on eBay are the double-pole e-stop switches although I'm not too worried as I reckon that a n/c contact is more likely to work when it gets thumped in a hurry than n/o. While safety is important, I'm not building a machine that will be used by a numpty on piecework. But we all draw lines in different places...