Personally, I like not using one, as it allows oxygen levels to increase at night, when plants and fish need it. Injecting CO2 without light makes very little sense to me. As a scientist Ray, wouldn't you agree?
CO2 is a fertilizer, not a pH balancing agent, so why treat it as such? fluctuating pH is not harmful.
At the very least, it's just wasting CO2.
And as for my 2 cents, I don't think they were personally attacking your decision to buy one Ray. And asking that only people who own one to give input is a little silly. I don't own a substrate heater, but I can tell you using one is ineffective. Similarly, using the reasons stated above, I can give many reasons for not using a pH controller.
Hoppy - as always, very well said.