I have the E300 in my 65. So far it's been great but i did go ahead and put a Fluval M300 on the other side of the tank by the filter inlet in case I need it but haven't so far! I have thermomenters on both sides of my tank and the temp stays consistent with what the heater is reading.
The only complaint i had about this heater was when i first set it up i was constantly getting a "LF" error, even when i placed the filter output directly in front of the heater. I finally unplugged and plugged it back in and haven't had a problem since!
Saltwater: 120g Mixed Reef :|: 20g Mixed Reef
Freshwater: 93g Planted Community
Other: 100g Amazon Milk Frog Vivarium :|: 40b Ghost Cornsnake Terrarium