I have it on my skimmer, as well as a recirculating CO2 scrubber. Some things to keep in mind that weren't obvious from the packaging:
* It floats pretty strongly, so you have to store it somewhere dry. I had planned to store it next to my skimmer but I had to put it in a remote part of my cabinet instead.
* Make sure the drain is a straight shot. When I first set it up there was a very subtle drip loop that I didn't notice that ended up getting stopped up until I fixed it.
* The lid for the carbon is vented. I don't know how much it matters for the air exchange with the recirculator, but it seems like air could enter this and travel to the main cup of the skimmer and interfere with recirculation. I have mine connected to a ball valve to open/close the recirculator based on pH, so I went ahead and covered the holes so I could more easily adjust this. You may not need to do this, but the CO2 in my house is over 1400 right now so I did notice a bump in pH when I did this.
* If you have a Reef Octopus skimmer with the automatic shut off valve in the normal lid, the auto-shutoff for this is different and kinda bulky. I had to de-solder the shut-off to get it out of the old lid and attach it to this one, then re-solder it. That worked pretty well though. If you have a different skimmer you can use the auto-shut-off that it comes with without issue.
* It doesn't come with drain tubing. You'll have to get a few feet of that. I got a few feet of 3/8" ID food grade silicone tubing which works.
Overall I like it and I'm glad I installed it. If you have an overflow in your skimmer it'll get shunted away into this and not risk getting the CO2 scrubber media wet and it makes it easier to go longer periods of time without emptying the skimmer cup.