Excellent!

It is gratifying when your experience on the ground dovetails with my design instincts.

If the contract calls for no more than 15 minutes no more than 3x per day I'd have their A$$ about the second time the Utility exceeded that. I'd beg, borrow, buy or steal a recording power analyzer and file complaints with state utility commission / consumer protection bureau / attorney general.

I'd demand they produce the records of operation of the interruption system.

Or, since the utility has seen fit to toss contract law and ethics aside, I'd set up an auto transfer switch to feed the interruptible panel from the main panel whenever they interrupt. Let them try to get a search warrant to prove that setup...

That's what generally happens (the by pass route). While I don't have a terrific amount of moral angst on that, I don't care to participate. The 3 times/day rule does have guidelines under which it can be broken (int. service essentially falls under the no free lunch rule). I've also had relay chatter from their equipment cause problems with mine and utility wire men blow transformers on my equipment through mis-wires.
What it comes down to is somebody else handling your low voltage wiring and turning equipment off whenever they feel like it. No thanx. In the usual AC application, around here, I'd argue that you don't run air conditioning to save money anyway.
There might be some advantage with the geo, but there is the other plan that discounts water heater as well as heat pump and is never interupted; but yes it charges you more in the summer when you use heat pump least (in MI)
J
Int. service is contracted for heat pump or AC only.