I tried Rigelian this evening.
1. No cover art ... at all. No idea why. I left things at their defaults, other than to change the default cover art name from "Folder.jpg" to "folder.jpg". There is a field called coverart prefix, but I am not sure what it does. Anyway... nothing I tried produced album art anywhere in the app.
2. Rigelian does an incremental pull from MPD as you swipe into a collection. This differs from Soundirok that downloads the entire MPD database and album art cache, all at once. With my 17K track collection and an iPhone X, this takes maybe a minute - one time.
Conversely, with Rigelian, you are treated to a spinning cursor everytime you swipe down into an album collection. I presume that eventually it caches the entire library.
Yes, I know that Soundirok's approach has been a problem for some in earlier releases - unable to fully process large libraries - but the perpetual wait cursor while swiping down into a collection is like Chinese water torture.
3. In-app Purchases. To browse by genre, I have to buy the app. I can't try it out to see how it works, first?
To the author of Rigelian: it's a different world than when you developed MPoD. The audience for this app is s-m-a-l-l. So, offer the best initial experience and then offer a purchase option after a trial period, if you must. Frankly, you should just make the app full featured and charge right away. It's a better experience and it will encourage folks to figure out the settings and persevere.
Just my $0.02.