What about if somebody doesn't use icons at all but just name mode?
I simply believe the Magellan's filetype editor and its context menu system is much more advanced then DefIcons system. And, off course, you can achieve the same aim on different ways.
Regarding to DiskImage, I found the latest version from Aminet as buggy, it simply hangs up my system, it is version 52.31 a.f.i.r..
Another story is I've got HDF filetype back. It simply mounts on doble-click there the same way as ADF and ISO images. I use diskimage.device 52.29 there and it works smoothly...