I quite like that! - It certainly fills the usable space nicely on my monitor, and looks (to my mind) less obtrusive and somehow "tidier" than the Toucan theme.
I can imagine it would allow for multiple image thumbnails to be horizontally located rather than vertically, making them easier to see (less scrolling).
Also, on the forum page, in this theme, unread posts show up a lot more clearly: -
I would think that with suitable UK Fungi specific customisation, it would look very good.
I use a desktop PC when viewing UK Fungi, so not sure whether this theme would cross over to small smartphone user's screens as nicely?
Obviously, to further site development, things need to go with what the majority deem best, so, happy to go with whatever the consensus ends up being, and with however you want to continue the site development.