I have been looking into making a temperature regulated fermentation chamber and I have been looking for something suitable to use. The STC-1000 temperature regulator is inexpensive and would do it very well if combined with a suitable chamber, preferably stainless steel and a peltier cooler and heating element. That should provide excellent control of temperature in the range that is required.
I have an old broken microwave convection oven that I could use but the chamber is a bit smaller than I would like. The thermoelectric mini wine coolers/fridges look ideal but I do not want to be buying a new fridge and then gut it. I would like a glass door on the chamber and most wine coolers do have that feature. Size is about perfect too, if only I could find a none working/faulty wine cooler at a low price then it would be ideal. However finding such a thing is not going to be easy.
Yoghurt makers are quite poor at what they are meant to do because the temperature regulation is very poor. If you read the reviews on Amazon etc, there are many reports of high temperatures and those are only the people who actually test it which many do not. It's only when you test them that you find out how poorly they perform. Ambient temperature can increase the temperature dramatically because they only contain heating elements with a thermal switch. Not much use if you need low temperatures to culture organisms which prefer lower temperatures such as B. Subtilis.
I would not recommend any yoghurt maker because I don't think any are any good for culturing/fermenting.