Yeah, I have resorted to Eagle 20 a couple times over the years when I had some PM that I couldn't get under control. But the fix was pretty easy in the end. Top to bottom sanitization, filtering intake air through a high quality furnace filter (which I change monthly), and just being diligent about keeping things clean. Since then, zero PM. But those mites were legit unkillable. The only thing that would get their numbers down reliably was a custom home-made mix using distilled water, 35% peroxide, 99% iso alcohol, castille soap, and a little peppermint oil. That would kill them, but is also hard on the plants. And you had to keep doing it every other day for weeks... but then a month later I'd find a little cluster of mites again, so eventually I just tossed everything.I've had to take the absolute nuclear option of saving some really old gems on the past and went full on eagle20. As long as they aren't flowered out for almost a year or so and new cuts are repeatedly taken.
Makes me sad thinking about it again.