I can advise the 6mm is seriously wide even on M4/3

Some might have a use for it but I am not quite sure what it is. I have used the Sigma DC 8-16 zoom focal reduced and there are times when fly specks in majestic scenery at 5.6mm can be interesting but at least the Sigma can be used all the way out to 16mm as well.
It's definitely way more niche than 8mm or even 7mm, the difference may not sound like much but it's drastic in practice... You can always crop in a little tho, avoiding it's worst flaw (vignetting), it would still yield like ~13MP cropped to 7.5mm. I think I'd rather have a very very wide prime like this as a complement to one of the native UWA zooms than lug a relatively larger & beefier DSLR zoom on an adapter, but that's very subjective.
I'd use this like I use my fisheye, throw it in the bag for when I think I've found one of those unique shots it'll really shine with, they're small enough to not be a bother otherwise or make me second guess bringing it if I'm using a larger bag.
I do have the compact Laowa 7.5/2.0 which is wide enough, tiny and compact for my prime shooting needs.
All I can get around here is headland and beach and more headlands and beach for hundreds of kms and they tend to look much the same after a very short while. Australian bush itself has a certain sameness also and representative images whilst can be excellent in their own right can also develop a sameness after a short while.
Quite a different genre and maybe not as arresting as the rocky outstanding scenery that can occur in many other parts of the world. This can provide impressive views with a very wide lens. But the rule requiring a subject in ones images is quite hard to find in wide angle shots of something that is just a sameness from wide corner to wide corner.
We can usually find something in an image that stands out as worth capturing but I have found out that many rural scenes in Australia work better with some telephoto to centre on and interesting subject somewhere in that bland nothingness that a wide angle could not distinguish enough to be seen as subject matter.
When the scene has a subject that is too small to be noticed it is hardly enough to exhibit your image simply noting that there is an interesting kangaroo in there doing handstands if you look close enough.