You need to run multiple iterations over multiple hours. Sometimes an error won’t get thrown until a later pass.
Yes and no. It uses Prime95, but cycles the load to simulate different transient loads that can make undervolting unstable. Running Prime95 continuously as a stability test is pointless for undervolting, as crashes occur during fluctuating power loads and not during full power. You can pass Prime95 all night with undervolting, then get a BSOD opening Chrome.