The “unbreakable” magnetic switches are described here:
For the Arduino power, I cut a small hole for the standard jack plug and power it externally with $5.50 power supply obtained from Altronics.
So far - no trouble whatsoever: if the code brings my machine to the wrong position - it stops and lights an LED. Naz never hit metal-to-metal (fingers crossed)
Homing is reliable within 0.5 mm (or less).
For each run, I include a “reference tap” - a 0.3 mm drilling/tapping the material at X-5 Y-5 mm. Thus, the homing accuracy can be checked with tiny angle square.