Thanks for your update and details about the Symfonium app. Sharing your experience I'm sure will prove helpful for others too. I may give it a test drive and compare it to the 3 that are in my usual rotation - GoneMAD for casual listening with the best browsing UI, Neutron for my critical listening moments, and occasionally Poweramp that sits somewhere in the middle (I like the Wavebar when playing).
There are many more players on the Android platform, and each one tends to have at least one specific core feature that they excel at. Some have a wider focus and do a great job on many player requirements than others. I did try to limit my efforts on those that used a "better" library management mechanism than the standard Android API. I started the thread based on some common themes here with users of mp3tag that revolved around using the standard player included by default with the device. Often those are very limited in functionality when it comes to utilizing the benefits of a well curated and properly tagged personal library. There is a similar thread for iOS players, but the list of decent players on the platform seems far more limited so far.
I have trended towards those players that are focused on a local library, since that is almost exclusively what I use and would show the most benefit of working with mp3tag. I have about 25k files in my library on a 1TB card, mostly in lossless ALAC format (for comaptibility with the other members of the family that are iPhone users). I have some older mp3 files lingering from the past, and also have some FLAC and DSD files for reference as well. This is broken down into about 800 Albumartists, 2k Albums, 50 Composers, and a mix of about 40 Genres. Scan times for local files vary by app but seems to run around 10-15 minutes on my current device (iBasso DX160), this only comes into play when adding a new app, as re-scans in most apps for new files is usually very fast. And lyrics to me are an irrelevant factor, so not something I have ever needed or tested.
Feel free to add your comments and experience with any of these apps or others as well!