Another point to consider, the farther the run of plastic tubing from your sump to the chiller and back, the greater the line loss due to ambient room temperature. Sit the chiller as CLOSE to the sump or aquarium cabinet as possible. You could use pipe insulation wrapped around the tubingrun(s), but this is rather unsightly and not really necessary unless living in a very hot/humid environment.
Operation is straight-forward. Remember to keep the flow fast enough to prevent freezing of the coils inside the box. If equipped with a thermostat, your fridge/chiller will be easier to control. Some models only allow you to set the main box temperature, not the freezer compartment. That's another reason why I removed the aluminum ice cube divider and tray. The probe that is attached to the wall of the freezer area will now monitor the entire cavity. Try to use opaque tubing to eliminate algae growth from the sump to the unit and back. You will probably get the black, smudged variety, not the bright green that we see in and around the lighting canopy. I used the milky-white, semi-transparent variety of hard, plastic tubing and experienced this build-up after 6 months or so.