I did go ahead with it .... and LOVE it !! I can ride in the arena with zero / 0 / no dust, AT ALL. No dust on my boots when I long-line, no dust on the horse's legs, no dust in the air, no dust when I drag.
The installation was easy and it has worked into the footing beautifully. If you did not know it was treated, you would not be able to tell by looking or feeling the footing ... not greasy or oily. The estimate is that it will last me two years before I need to re-apply some, but that the second treatment will be with a smaller amount. And having watched how it was done, I believe I can do it myself in the future -- just need to buy a sprayer unit of some type.
Yes, it was pricey ($4,500 to deliver, install, and grade a 60x20 meter arena), but my contact lenses and lungs say it was worth it. And the company was a delight to deal with ... we traded lots of emails getting questions answered, footing analyzed, etc. They were prompt and supportive without being pushy.
"Avoid loud and aggressive persons, they are vexations to the spirit."
- Desiderata, (c) Max Ehrman, 1926