"non-merged" doesn't exist anymore.
People often forget:
First of all, if you have a datfile without any parent/clone relationships, it doesn't matter which merge mode you select, they are all identical then. Users tend to say "I need not-merged mode since I don't want them split or full merged" but they're using a dat which doesn't even have the possibility to do merging.
If you have a datfile (e.g. MAME) which has parent/clone relationships, split, full and standalone do differ of course.
Now a bit background story:
Let's get back in time to see where this "not-merged/unmerged" mode came from. In the early years of MAME when merge modes came in, not-merged simply meant that an archive contained all the files which represents the machine, no matter if it's the 10th pacman clone which has 99% of file in common with its parent. So not-merged gives you a bit of a full set, something which can be carried around and works. Then MAME started to include and separate bios sets. Some sets have a dependency on bios files, too. So they aren't included in the not-merged sets. So e.g. if you want a neogeo game game like metal slug, you already have 2 archives, one with the bios and one with the mslug roms. So at this point "not-merged" started to be not really useful. Later on MAME separated devices, too. So again, even if you have not-merged sets, you'd need multiple archives to represent one machine.
With (the new) clrmame, I dropped this mode completely and added the "standalone" mode. This mode adds all dependencies to each set (parents/bios/devices), so you end up with one archive which can be carried around and works. Surely (as the not-merged mode before), this is a total waste of disk space.
To sum it up: non-merged -> not really making sense, standalone -> does what is expected
I'm of course open for discussion on this...