You will be happy with your decision...it's the best available heater setup.
There's some debate about having to waterproof the temperature probe...some use a shrink wrap on it to seal it, others use the temp probe as is. I've been running mine without the shrink wrap for about 1 year with no problems, but I would feel more comfortable if it had the waterproof shrink wrap on it. Come to think of it, I really need to shrink wrap mine. Better to be safe than sorry.
Placement of the temp probe is pretty important.
In a setup with a sump, it's best to place the temp probe upstream from your water flow, but it should be in the same body of water as your heaters. What I mean by that is that if your heaters are in your sump, the temp probe should be in your sump. If your heaters are in the display tank, the temp probe should be in the display tank.
The logic behind this can be explained by the following 2 scenarios:
Scenario # 1
Heaters in sump, temp probe in display tank: if your pump fails and water stops circulating, the temp probe will be monitoring the display tank water. As the temp in the display tank drops (remember, water is not circulating from your sump to the display), the controller will fire on your heaters in your sump. The heaters in your sump will remain "on" even though your sump may attain near boiling temperatures since the temp probe is measuring water in the display tank. The outcome for bio-media in your sump is not good = boiled. If the temp probe is in the sump and heaters are in the tank fish will be boiled.
Scenario #2 (the correct way to setup your heating system)
Temp probe and heaters both in sump. The temp probe should be placed upstream of heater location. For example, if water enters your sump on the left and your heaters and return pump are located on the right side of your sump, the temp probe should be to the left of the heaters. This configuration is best because given the water flow through your sump, the probe is measuring the temperature of water farthest from your heaters (it's measuring the temp of water draining from your display tank to your sump). The other key benefit is that during a pump failure, the temp controller will fire on the heaters until the sump achieves the set temperature at which time it will power down the heaters. All is well (temperature wise); this configuration avoids a boiled sump or display tank.
As seen here, probe is upstream from heaters:
As others have mentioned, as a failsafe, you can set your Jagers a few degrees above your desired temperature setting on the Ranco so that if the controller fails in the "on" position, the internal thermostat of the Jagers will power the individual heaters down when that temp limit is achieved.
Another tip is to use a piece of tape to fasten the temp probe wire so that it does not inadvertently pop out of the tank. I have read horror stories about people inadvertently popping the temp probe out of the tank and if this goes unnoticed the results are not good (the air temp is usually a lot lower than our tank temps, so this can be catastrophic).
A little piece of tape can be a lifesaver for your fishes.
Hope this info is helpful.
