I don't know yet
As it was very quiet on the pms side for the last year or so and I had some spare time, I siezed the opportunity to give ums a try. They've made some interesting improvements, especially better renderer support and a cool web interface to browse and stream media. On the other hand things like the resume file functionality have been added which don't really fit the media library implementation.
Unfortunately I won't have a lot of time working on this in the near future. My preferred solution would be to propose a new plugin FileProvider which would allow to choose either the default browsing by file system or the media library (or any other future implementation). This would fully decouple my implementation from the streaming functionalities and would avoid having to maintain a full parallel build for mlx. We'll see
If you want to try the ums-mlx build, you're not taking any risks. It installs into a separate folder and uses a different profile directory then pms-mlx. If you want to use your current folder configuration, you can copy your database to the profile directory and rename it.