Thanks to Apple's exceptional software quality the app has plenty of bugs and good luck exporting a lot of files out of said library - you're in for an endless game of spinners (it does some network IO on the main thread), "not responding" and memory leaks.
But hey at least we've got Liquid (gl)ass now.
Worked well for me for 70k photos but took a long time
> Thanks to Apple's exceptional software quality the app has plenty of bugs…
I use Photos for macOS daily and I've never run into a bug with my 50K+ photos library. (To be fair, Photos doesn't do that much, and I use it more as a master catalog with Aperture's spiritual successor Nitro.)
> …and good luck exporting a lot of files out of said library…
Not sure why you would need luck to copy the "Originals" folder from the library package.