It really depends on what you are looking for. The Johnson Controls and the Rancos are simple on off thermostats, where the Spyderrobotics and thermostats like the Helix are proportional. The difference being is a proportional thermostat controls the output voltage to your heating device, so when the temp starts getting closer to your target the amount of voltage being output keeps decreasing. This allows for the highest degree of accuracy and I would say helps in the longevity of your heat source since it is not going full on all the time. Thermostats like the Johnson Controls and Rancos turn voltage off at your target temp then wait for the sensor to cool anywhere between 2 degrees and .5 degrees (depending on brands) then turn the voltage back on full. This is great for certain application and great for use as a backup to a proportional thermostat. But again the proportional thermostat is going to give the best accuracy.
As for the other options you listed the Spyderrobotics Herpstat II and Pro both have the capability of hooking to the computer with a proprietary USB cable and software. This allows you to check temps on line and can be setup to e-mail you or text message your phone if your temperatures go out of range. Of course this relies on your computer so if you computer crashes or is off line then the feature is disabled. All the Herpstats except for the original also have built in audible alarms as well.
Hope this helps,
George Knaack
GLK HERP
Also here is a post I found from Dion the owner of Sypderrobotics that talks a little about reliability and lifespan, I have posted this here before under a different topic as well:
“One thing to watch out for in the small cheap thermostats is heat. We all know heat is the killer of electronics and the majority of the under $50 thermostats (the one in question, 500r units, ect) use what is called a Triac. All the wattage runs through this component and is the same component used in proportional thermostats. The difference is often the cheaper products use a component that is to spec but do not necessarily count for all the extra heat. Those have small packages with little room for circulation. When a Triac fails it has a high chance of failing in the on position. So keep an eye on the heat of the case and make sure the thermostat is mounted where it can get airflow. The cooler, the longer it will last. We take the other approach and assume the spec is not enough and overbuild everything to prevent this. Where a 5amp triac could be used we put in 15's. They take more heat and handle voltage spikes where others would fail. Its like having a Hemi in grocery wagon. You don't need it buts its nice to have just in case. Since the heart of the circuit is overbuilt we have the fuses there which should trip before something like this happens giving the much preferred "power off" failure. That being said I believe the ultimate setup is to have a relay based thermostat directly into the wall(think ranco or johnson controls, maybe us one day) and then a proportional thermostat plugged into it. This way should you ever have a lightning hit, voltage spike, or just a faulty component in the proportional (or any triac based thermostat) the old fashoned relay thermostat will take over and save the day.”
