Eheim certainly has the track record as the most dependable and reliable filter available. We may all have our filter preferences, but Eheim has been around several decades now and their filters have stood the test of time in this regard.
To the heating unit in the filter. In 1997 I bought a new 70g tank, and I decided to get the Eheim Pro II canister with the heating element in the bottom of the canister. This filter/heater has been in operation ever since, continuously, and I have never had an issue. I have had it on my 90g for the past six years, and the temperature in the tank never varies by more than 0.3 degrees from the set temperature--that is less than half of one degree. I have two regular heaters in my two other large tanks, and they are not this accurate.
The heating element in an Eheim canister is no less likely to fail that any submersible heater, and perhaps far less likely. The filter was higher priced obviously, but at the same time I didn't have to spend money for two "regular" heaters which would likely have been comparable if not more than the additional cost. And having the heating unit in the filter means that all the water circulating is heated, something you cannot guarantee with regular heaters. And you don't have two more pieces of equipment in the tank. For a 4-foot 55g, you want two heaters, one at either end next to the filter intake and return respectively.
I have not tried the inline heating units that apparently can be added to any canister.
Byron.