I'm glad I found this post as I had a similar question. I've been out of the hobby for several year, and part of that was due to the catastrophic failure of my HOB refugium/protein skimmer. After working beautifully for 2+ years, it suffered a catastrophic failure one night and I lost the tank. I love the idea of a refugium, but I won't do HOB again. I've been tinkering with the idea of converting the back 4" of my tank to a build-in refugium, and it would be similar to the Fiji Cube AIO Box linked above.
What is the community opinion of in-tank AIO systems like this?
Regards