I noticed one tank that drops 2 degrees F when I turn the heat down when I leave the house. I have the E series on 8 tanks and only one tank has this issue and only when the house drops below 65 degree's. The rest of the tanks are in the basement that doesn't get cooler than 72, even when I lower the heat for the rest of the house. I'm not sure I can fault the heater for my house being cold. And the heater my be undersized for the tank, I have a habit of buying smaller heaters.
i had (well its still in the tank actually) a e300 in my 106 my older house would get cold. like mid 50s and the temp would drop to the low 70s. so i had an extra jager 200w that was going to go into my 220. Added that and it heated the whole tank on its own and the e series never even came on. worst it would get was down to 75.
On my 220 i run a 300w and 100w jager and it stays at 79 no problem.
for the price vs performance the ebo is much more quality than the e series.
and they are cheap... dr. fosters... just get one you'll see. my tank is near 2 windows and it's 22 degrees F outside....warm today...