after an hour on the phone with the manufacturer (Dave, has been really great in helping me figure out my strange install situation!) going through wiring step by step, I had to reroute some hoses.
Particular issues with the unit:
1. 30amp GFCI breaker required at 220V
2. he sends you a little transformer (doorbell type I think) that gets wired in to make the Flow switch trigger the GFCI
3. Heater must go between Pump and Sand Filter, as his service calls over the years have led to finding a VERY small amount from the Sand filter contributes to some failures?
4. Heater has an air port/valve that has to be up and fairly level should any bubbles get trapped in the unit.
My garage set up makes it a bit strange, but I am expecting to be testing flow, GFCI trigger, and Heating power today and tomorrow to be sure it's all going to operate as it should and be safe like it should.
So if you have a cartridge filter: few issues. If you have a sand filter: you need this BETWEEN the pump outlet port and the Sand Filter inlet port.