Some changes are happening !

The RES-15 has a pretty low hysteresis and high power draw. The RES-64 is bulkier and only SPST but who cares ? The hysteresis is more than 2V under 2mA only so it is better suited, more stable and resilient, less power-hungry...

The testing strategy does not change but some electrical parameters do. Mainly it's the series resistor and the voltage range. The RES64 has a 2K ohm coil so a 10K series resistor increases the resolution by ×6 and the voltage shoots up to max 36V.