The UI for the composer is really quite bad, it slows down and becomes clunky and barely usable after around 200 notes.

Dragging notes around doesnt seem to work half the time.
When trying to copy and paste notes, they're usually pasted somewhere way off screen that you'll need to zoom out for to find, never in the right position and then combined with the above half the time you cant even try to move them into the right spot.

Scrolling left/right or up/down is slow and freezes the UI a lot.

Please fix it.

Hows everyone elses experience with it?

For me it's the black spirit dice. Every time I roll it's like the laggiest thing ever and is the reason why I stopped at 100 stages with 300+ dices. Mind you I have an enthusiast grade PC built last year with a 3080RTX but the UI can get really awfully slow. I believe they use MS Edge web browser for some of these things but Edge supports GPU acceleration so it should be fine in theory. I know it's a shot in the dark but maybe Edge needs to be updated? I probably should update mine but it's spooky just to look at the icon. lol

Yes the composer was awful to work with, it saves your files to your drive. Yet will not allow you to edit them with a decent midi editor or enter music using a midi instrument.  I have recommended somewhere in these forums to use a piano roll on YouTube.  Here is a simple example of what I talking about.  Piano AccoMan's channel is loaded with TV show tunes, movie themes, but mostly geared to teach little kids to play piano.   The issue using the piano roll is the key board in most videos, such as this, needs to be rotated 90 degrees counter clockwise, and errors will be all too common and frustrating for people who don't read sheet music or play by ear.  

I really wanted to use my midi keyboard to compose some original music.  They even held a music contest recently.  I don't know who won, but I wonder, if the pure frustration caused by the lack of a good editor was worth the win?  I do appreciate them having an ingame music editor, but it needs to be improved, if they expect something other than knock offs in their database.  

Oh by the way, you absolutely need a Shai at level 58, a C rank or higher in music score, to make anything worthwhile.  Otherwise the limitation on bars and notes at the start, will be very short Johnny One Note songs.   

Have fun!