There are certain things that you should spend money on. Other things, not so much. This is one of those things to spend money on. $115 + tax. A salt bath annealer. It will keep your brass happy and un, de or reverse work hardened. It's especially good for those of you that shoot cartridges where the brass is hard to find. https://ballisticrecreations.ca
If you have no equipment, this system is less than $200 CDN. Which includes the salt, thermometer, case holder and Lee pot. I have been salt annealing for awhile, and it beats the candle method to bits. It is faster, and much easier on the fingers. Watch the video.
I have one of these. It's a Lee Precision Melter. I did use it for melting lead, but it got repurposed to anneal brass. Sadly, it gave up the ghost after many years of dutiful service. So, I had to order another from amazon. $60 plus free shipping.
I know what you mean. I am not a metallurgist, but when I read their test, I was struck by two things. First, we call this process annealing, but I think we should be calling it stress relieving. Whether done with a salt bath, a candle, or electricity, you are relieving work hardening of the brass.
Like you, I wondered if this wasn't self serving. They are selling a product. While they are not lying about annealing metal , it could be interpreted that they are not telling us that stress relieving is done at lower temperatures, and "salt bath annealing" is another way of accomplishing this.