After a couple of months trying 2-part bromine, I'm giving PristineBlue a try in my 320 ga. fiberglass spa.
The only people who use it are my girlfriend and me, so the kill time is not such an issue, and I figure I can always pour some bleach in if we're going to have guests.
So far we are both happy with it compared to the bromine.
Things I did not like about bromine were the smell and the water feel. Also, after about 2 weeks, hitting it with MPS would no longer create an active bromine residual, requiring dumping more bromide salts into the tub.
I got tired of smelling like bromine when I got out of the spa. I also never felt in control of the chemistry, and wound up testing the water a couple of times a day. And we went through pounds of MPS. I wound up shocking with bleach toward the end of the bromine run because I got tired of buying MPS.
So far the only negative with PB has been some greyish staining that happened around some of the blower holes after a week, but I took care of it pretty quickly.
The PristineBlue start-up instructions only call for adding PristineClean, their metal sequestrant, at the 1st 2-week interval, not at start-up. I added the recommended dose as soon as I saw the staining, and it got rid of the staining in a matter of minutes.
With my current understanding of water sanitization, I would be leery of using the stuff in a pool, but I think for my private spa, it has potential.
We both have noticed that our skin feels softer now after our marathon soaks (we spend at least 45 minutes a day in the tub, with the heat topping out at 102).