I will never use a hovabator again, but the failure mine had could have probably been prevented. I had one going on its thermostat, and we had a power outage, and the hova went back on and the temps skyrocketed past 105 degrees. All 8 eggs inside went bad.
I hear all good things about NS incubators, though I have never used one.
I made my own incubator out of a styro cooler, flexwatt, a great Helix thermostat, and a few soda bottles, adding egg boxes and thermometer of course. It worked like a champ and I will never use anything else! Your incubator is only as good as is thermostat.