Rhyno, one factor in the heat signature of M625 is the automatic self biasing of the device. For what I understand, as the average throughput rises, biasing moves more towards class A. On the other hand, idling power appears to be much lower, indicating that the biasing may readjust downward as well.
One more factor is the high compactness and circuit density of the device, hence the relatively higher heat dissipation per square inch. If the device were larger, skin temprature would be deceptively lower.... 100W idle consumption per the specs at:
Concerning long term reliability, we can hope that M625's behavior is similar to older high bias JRDG designs.... Anecdotally speaking, as far as I know, my former JRDG 7M monos are still making music without issues over 20 years since they left the factory.
Rhyno, do you live in Houston? ... So does David (Kawika). G