I'm quite sure that I've taken and published more Brix readings on cannabis plants than anyone else on the forum, perhaps anyone else at all.
For well over a year I took 2-3 readings on each of 7-8 plants every week. Now I only do it sporadically. If a plant looks unusually good or bad I'll check it out, and I still get a reading at harvest. For a long time, I've thought it was unfortunate that Doc chose to name the method High Brix, since none of the users, including Doc, take Brix readings any more often than I do.
All this crowing about how great HB is, and no one even measures it.
A refractometer is just a tool, and the readings are just vague measures. The important part is the soil composition. If you start with the mineral ratios that the Kit is designed to provide, you'll have an advantage - it doesn't matter how you get there. Then, since we know what's in the soil, we can use custom foliars and drenches. Anyone can do the same. Or create your own soil composition as always, and use nutrients designed for that soil. "The Kit' is just an easy way to do that. And it typically turns out well above average.
I recently compared it to machines at the gym. If you want to use free weights, great - they're the best. But if you're not sure what you're doing, if your joints and connective tissues aren't strong and well built, if you don't have a spotter ... etc ... machines are a great way to do the job without worrying about something going very badly.
Brix is a canard. It's not what makes the plants turn out so well. My whiteflies have always descended on the least healthy plant tissue. They distinguish between plants and between leaves on a plant, and they always go for the yellowing leaves and the weaker plants. The rest show no sign of being bothered by them. I doubt if there is much difference between a 12 or 18 Brix plant, but I'm sure there's a difference between a 6 and 12 Brix. Whiteflies would kill a 6 Brix plant in a week.
And lastly, Brix reads dissolved solids -
ALL dissolved solids, no matter what they might be. Some of them don't necessarily contribute to plant health. The point is to use it to compare different plants under similar conditions. They should all be healthy in the first place. A Brix reading can tell you when one plant is lagging or doing better, and then you can adjust nutrients. It's a quick and easy test.