For me: uploading single file using their client ~25MB/s, downloading ~50MB/s (30-60MB/s).
In newer versions of their linux client it's possible to mount filen as network drive or to start webdav/s3 server.
It depends if your reverse proxy is inside your home network or outside. It should work without any other configuration if you forward ports 80&443 from external domain with something similar to rathole and configure reverse proxy inside home network.
Here's the reason for the slowness described https://f-droid.org/en/2025/08/28/twif.html
About onion - they would not work without tor enabled.