You can keep banging your head. It looks fun. I read your post though. I'm also very versed in how a solenoid works, and how to figure out the cf of co2 to bring a given area up to a specific ppm value. See no reason to buy an "electric regulator", as you call them, since for under $60 he can add a solenoid and flow meter to his regulator. And yes the co2 controller isn't needed, but makes things much more consistent. Plants acclimate to the highest stable level of co2. If there are wide swings due to not properly tuning his gas/vent cycles, co2 supplementation can be less than efficient, or at the worse, a wasted endeavor.
I still wanna see this $200 controller someone spoke of.