I am currently falling further in love with this media by the day. I was introduced to it by @Will Lutman with his AIO that included a little can of the media and a chamber designed to tumble it. With very little rock I was able to keep the tank very balanced.
This is a great video on the media in general (but it's made by the manufacturer, so it also potentially propaganda)

Note they reference that the original plant to use it (potable water treatment is the primary use) is still using the same media they started with in 1989. It is not consumed but rather colonized by the bacteria that would normally be restriced to live rock. It requires down flow to tumble because is barely positively boyant. This is counter intuitive to our general media, but once you turn off the return and see how easy it is to clean the chamber under the media you'll probably be as hooked on it as I am.
Based on my use so far I have to say it appears solid as a replacement for much of the "required" live rock we generally use. There is no possibility of overdosing. If it leaks into your tank it will just float to the surface or grow zoas on it. It does not degrade and it's about $20 for more than you will need in your life. On my temporary 40b/55 system I've simply reversed the flow through the sump and threw the k1 in the first chamber with an acrylic grate keeping it in. I probably needed a few more holes in the plate so I added an air stone under it to help send it back up instead of sticking to the grate. As long as it keeps moving it keeps working.
Here's a quick vid of my current jerry rigged chamber. This is all temporary as i build my new system, but having it right in the drain section definitely seems to be the route I'll go on my sump for that. I would definitely love to hear if anyone has any horror stories on this stuff, but so far I think my opinion tends to be the consensus among those that use it (like Shedd and the folks that clean the water we drink).

The darker colored pieces are seed stock from my Lutman to help get things going and it does take quite a while to start coloring up so I would not recommend just pulling everything else off your tank and starting a fresh k1 reactor. Right now I'm only running that and a skimmer and live rock (and a random ball of chaeto I picked up at the swap) and I'm able to procrastinate water changes far longer before I start to see algae on the glass. I'm still keeping an eye on it, but so far