Can someone please explain...

[Delphinus]

It totally depends on what I'm trying to do, which affects my choice of what glue to use. If I'm mounting a clean cut frag of SPS onto a disk, unless I have a poor surface to work with I'll just use cyanoacrylate (superglue) gel. If it's an odd shape then I'll use the epoxy. I've used the green stick, the Tunze stuff and the Deltec stuff. In my opinion they are equivalent products, except that the Tunze and Deltec epoxies harden in a brown or pink (I forget which is which) which blends into rock nicer than stark white does, but in most circumstances coraline covers it anyhow over time.

It's in the approach though - like Brad said, the stuff is filler, not an adhesive. So it has to surround the pieces, not just interface them. I did use it so mount some gorgonians to some rocks but I had to use elastics to hold the gorg bases down while the epoxy hardened. Now it's fine although the elastics are permanently embedded in the glue. Eventually they'll just disintegrate though.