Thank you for the write up. I haven't used songkong's reporting much as I typically work with jaikoz. I tried the demo of the report you have online. Is there any easy way to see what albums are missing songs to be completed, like how jaikoz does it?
I find it very handy to look at jaikoz report and see missing songs in csv view and quickly see which songs I might have tagged wrong or missing that are not showing up as missing on the albums I have loaded.
One suggestion, in the folder view, you have it setup so the user has to click on a very small triangle icon left of the folder for any action to happen. It would be far more user friendly to make it so that the whole row is a clickable spot. ie, the small triangle icon, folder icon, and folder name.
Also I noticed an issue on the left pane where you have the MusicBrainz Summary with the vertical expandable menu with all the letters. If a user clicks on a letter, it expands, and they see all the artist names that match that letter, followed by a lot of white space underneath the last artist. They then have to scroll down quite a bit to get to the next letter. This appears to be a css issue. It looks like you have:
removing the height property fixes the issue and makes it look a lot cleaner.