I have only bench tested them, they are not installed permanently on my layout yet. In bench testing, they were faster than the PH-180 that was the power source used for the test. I did several tests using the alarm, reset and optional LED's. Was shorting directly across the track several times for each test. They beat the PH-180 every time and passed with flying colors, a great little device. They trip instantly. (There was no load on the PH-180, and t be fair, I was using the 8 amp setting on the PSX-AC's.)
I'm not an expert by any means, but I think you would have a hard time finding a better and/or faster breaker. Not sure how badly they would be needed with the Lionel PH-180's as they also have excellent breakers. I would say that anyone using anything other than the PH-180's and running modern electronic engines might want to seriously consider using the PSX-AC's. (I don't know about the breakers in Z-4000's or the new ZW-L's?)
Even if you have the PH-180's (or Z-4000/new ZW-L), these would still be a great idea for added protection. $45-$50 for the PSX-AC is a lot cheaper than new electronics for any of the modern engines, and much less than a new engine. Got my PSX-AC's at Tony's Train Exchange (they have some additional parts for them also, if you want them). I found out later that Charles Ro now has them for slightly less than I paid for mine. They are listed at the end of their Lionel Legacy/TMCC listings.
If you search the forum for PSX-AC (or maybe just PSX?) someone did a video showing their operation a year or two ago. There is also another thread or two on them here somewhere.
