This is the route I took. Looking at it now. No obvious issues. I've used Arc Menu in the past so I'm familiar with the settings. Looks like the only difference is the "Display Arc Menu On" option and the customization of course.
I like the theming. It's clean and the position of the menu is how I would expect it to be with small margins left and bottom. One possible thing to consider is that the desktop windows have a heavier shadow while the menu's is much smaller. If a light window is behind the menu when you open it there is less contrast between the menu and the underlying window than there would be with two windows on the desktop. Not sure if it's possible to match the desktop but it would help with contrast. Perhaps if it was even just a little larger than it currently is.
If you set the panel location to either left or right, the menu icon takes up too much space.
I was able to correct this by setting the Menu Button Appearance to Icon instead of Icon and Text.
It also looks fine in the bottom position with the appearance set to icon so I'm not sure why it is set to icon and text by default. I assume Manjaro users will probably be using this layout via the new layout so this might not be a real use case but maybe worth changing.
Something else I noticed that is true in v39 as well is that when you activate the menu, you can't initially navigate with arrow keys. It looks like the focus in in the search box and unless you hit tab or backspace you can't use the arrow keys. Not relevant to this necessarily but I thought I'd mention it.
That's all I can find. Hopefully this is useful. Thanks for putting this together. Very nice addition to Manjaro's GNOME edition.