We have just hit summer, I use a reverse cycle air con cheap to buy and costs nothing to run.
As mentioned the temperature is pretty well constant at 16-16.5 C, it will creep up to 18.5 C on a 35 C day
I primary ferment in a 30L plastic fermentation bucket in the house for the first 4 days with a temp controller set to 20 degrees and a heat pad underneath the bucket. I then move it into the garage - on top of the heat pad, on top of a foam block - where it can get pretty cold. Same heat pad underneath the bucket, loads of bubble-wrap round the bucket. Keeping to 20 degrees is no problem.
As you say, heat pads are fine for fermentation vessels, especially if you can keep the environment temperature down. But I suspect the issue here is a temperature controlled cabinet for conditioning - for example, mine would be typically 12C - no problem in summer, as the fridge element keeps the temperature down, but in the winter the shed temperature can drop below 10C, so a low power heater is helpful to keep the fridge temp within desired limits. But it is a luxury not a necessity, I would agree.