How effective is anti-static device for LP play?

excellent questions. I can only comment on two. Dry definitely increases static problems, and Zerostat / Mapleshade Ionoclast / Walker Talisman and the like, do make a difference, lowering noise floor and increasing smooth transparency .

Stop using your carbon fiber brush, really, try not using it.

I "think",based on an intuitive approach,that we ALL see dust on LP surfaces,but even without using a carbon fiber brush,it "sticks" to surfaces.Yet,blowing on the LP surface(even in good humidity)leaves the dust in place.So,I assume there is always some degree of static present.Hence,even in good humidity the antistatic devices are a good thing.
Does this make sense?

I use the Zerostat and find it very effective. Dryness aggravates the static situation, but the mere act of cleaning the record pre-play will generate static. I use a carbon fiber brush for the rough clean, to get off any big chunks. I hit it with the Zerostat as I'm doing that and then I do a final clean with a microfiber cloth, after which the record needs another hit with the Zerostat.

The records generally have a low level of static when I start, but the cleaning, particularly with the microfiber brush, really generates a lot of static. At night, with the lights off it's very easy to see and I can feel it tugging at the hair on my arms.

Not only does it generate sound in some instances, but it attracts dust. So discharging your records is a beneficial process.

Dave