I’m on year four with one, so I guess that counts as long term.
For me it stuck around because I treat it as a helper, not the main act. I still run a normal chlorine residual based on my CYA, I still test weekly with a proper drop kit, and I still watch pH drift like a hawk. The mineral unit just seems to take a little edge off algae pressure during the hottest part of summer when my water temp sits around 86 to 88 and the sun is relentless.
What changed long term wasn’t chlorine demand as much as stability. My overnight loss is still under 1 ppm most weeks, but after heavy bather load weekends I don’t see green haze trying to form in corners the way I used to if FC dipped toward the low end. That said, I also tightened up circulation. I make sure I’m getting close to one full turnover daily and I clean the filter when pressure climbs 4 to 5 psi over clean. Without that, I doubt the mineral system would feel worth it.
The tradeoff is you add another number to watch. I keep pH in the mid 7s and pay attention to saturation index so I’m not inviting scale or metal staining. It’s not hard, just narrower margins.
So I’d call it sustainable long term if you’re already disciplined with testing and balance. If someone is hoping it replaces good habits or cuts chlorine in half, they usually end up pulling it after a season.