heating and cooling makes for a all season ferm fridge that can handle lagers and ales and D rest and cold crashing with ease, so yes you do need heating and cooling to have a fully functional ferm fridge in most parts of the country.
on the subject of set point vs beer point, this is an issue I struggled with after converting a fridge with an stc-1000 and a low watt heater. The problem is you set one temp and get another. Very frustrating. I had read about many probe placements in ferm fridges including themowell, air, taped to FV with insulation, Zip tied to a tall boy, and submerged in a cup of water. I went the air route because it was easy to implement and maintain however I was not able to adequately control my wort temp despite my best efforts. So I launched a study.
I used a bucket of water with a thermometer in it and recorded the following obsessively for quite a while.
STC set temp
CA value (temperature correction value setting on STC)
STC indicated temp
Air temp (inside ferm fridge)
The study was conducted in cooler weather using the heater with a set point of 65 F
I collected data for several different CA values at the common set point of 65 F
I carefully poured over, processed, deconstructed, and evaluated the data for the 5 factors and each CA value was compared against each other. results are as follows.
For my particular fridge, probe placement and STC, CA- 4 turned out the best results by maintaining liquid temp the same as the set point within +/- .25 degree (hows that for a "dumb" controller!)
All CA values maintained decent control over liquid and air temps (however far off they were), but the CA values closest to 4 did the best in that regard as well.
The air temp was often way off from the set point and liquid temp which is confusing at first, but once dissecting the data I realized that this did not matter. only set point and wort temp need to match.
That is the relationship that matters most. make them match and you are done. I REPEAT, MAKE THEM MATCH AND YOU ARE DONE. Air temp and indicated temp will bounce around will probably not match up or make sense at a glance (Temp wise). Just mind your set point and liquid temp at any given CA. its that simple.
The down side to using air for the probe is that the movement of wort temp is slow if the wort is not near set point.
That is to say that if you put your FV in the fridge with a temp 15 degrees warmer than set point, the fridge will hold your set point (since the probe is in air the set point is reached), no cooler.
This will take significantly longer to cool the wort than a fridge running full tilt (lets say 33 degrees) because the probe is in the liquid which is well above the set point, which in turn drives the fridge to keep cooling.
however if you are aware of and make sure to account for this short coming it is not a big deal, and saves fussing with thermowells and tape and such. Not to mention extremely accurate wort temps....
This is some hard earned info. Hope it helps.