Only thing it will hurt......
Possible Overheating
PRV lifting or constant dripping due to the overheating
No electric or propane should t-stat completely fail due to same set for both electric & propane operation
Relying on just the ECO to operate properly...if it should also fail then there is nothing to shut down heating source turning WH into mini steam bomb
Other than that.......nothing to worry about.
I operated commercial boilers for a living and there are redundant controls/safety features for a reason (dual t-stats, flame cut out, flame proofing, PRV)