Since I seem to be straight in your target group, and since I'm still looking for a good thinking tool, I took the time to write up my thoughts after trying the app.

I currently use two tools: GoodNotes and Concepts. Concepts is much better for drawing, with its layer system and the excellent "use your finger to lasso-select" tool. I love the infinite canvas, too. But Concepts requires too much fiddling. The tool palette can't be fixed. I would like to have the same tool and color palette in all documents, so that I can avoid wasting brainpower on fiddling with tools. Concepts also fails in organizing multiple documents — the viewer wastes lots of screen space and it takes a long time to find a document. I reported all this to the Concepts team, but they seem to prefer to compete in the crowded "drawing app" space rather than in the almost empty "thinking app" space.

GoodNotes is much better for thinking. I love the responsiveness, a simple tool system. Palette management is better in that I could set the colors once and have the same ones available everywhere. I still can't lock/save/export these settings, but as long as I'm careful, this works.

GoodNotes isn't perfect: there is a bug where the app opens with the list of documents rather than where you left off. To use the lasso selection, you have to use the toolbar, rather than use your finger like in Concepts. It has a weird concept of "paper sizes" (what paper?!) — I want to draw on a canvas which is exactly iPad-sized, with no panning, zooming or margins, but I always end up with either wasted margins, or fiddling around with zooming in GoodNotes. Document organization isn't that great — I want to quickly create multiple single-page notes and I do not want the app to ask me each time whether I want to save or delete my "Untitled" document. This isn't Windows 95, people.

Moving on to Muse:

First, to get this out of the way: $100/year is just fine. In fact, I could pay more if the tool became really good. It's a business tool for me (at a first approximation, I get paid for thinking).

I don't care that much about the emphasis on inserting images or videos. That's just not what I do. My notes are mostly drawings and text.

Inserting PDFs and marking them up is a very nice feature and I liked the PDF viewer initially. Still, it wouldn't work for me in practice: when designing electronics I routinely work with 600-page PDFs. I need the tool to remember the position, have a simple bookmarking system, and a way to quickly navigate to somewhere around page 400 visually. Also, no continuous scrolling, please — single page flips only.

I expected a double-tap on the pencil to pull up the eraser and it didn't.

I couldn't figure out how to pan the board (perhaps you can't?). I think I need either zooming+panning or multiple pages.

I couldn't figure out how to delete a card.

I could drop the card into a board (initial screen), in spite of trying multiple times.

The lasso system is way inferior to GoodNotes or Concepts. I'd rather have object-based selection, not one that cuts through anything. And I really, really like the idea (from Concepts!) of using your finger to lasso.

The tool colors are ugly. I would like to have my own palette (5-8 colors and at least two thicknesses).

I tried using Muse for actual work, but at the moment there is just too much fiddling around and I'd lose some of the functionality I now have in GoodNotes.

Summary: while price is not a concern at all, this is quite far from a good thinking tool for me, and the primary emphasis on inserting images isn't aligned with my needs.