With the understanding I've been brewing and drinking today;
According to Process Control & PID Technical Notes, for on/off control you need to manually set the P (proportional) band to 0. Looking at the TET612 manual (I have one for my HERMS and absolutely love it) the lowest P value is .10
So I'm thinking if you set the P variable to .1, you will probably get the on/off control you need for a keezer. The J1 and J2 are relay outputs and seem to be set up for alarms. The manual says 3A @ 220V so that should be 1.5A @110V. If your keezer is 1.5A @ 110, go for it. Otherwise you will need an additional relay to avoid an overload.
I've been thinking about doing this myself since the TET612 is so damn cheap on e-bay. I hate to pay as much or more for a simple on/off controller when I can get a PID and maybe us it on the brew rig.
But since I've been brewing & drinking, YMMV.