20% of privacy geeks I know swear by double VPN layering with Mullvad, but honestly I think if you keep your system clean and avoid leaks, one solid VPN like Mullvad is enough, tf.
Actually, I'd say like 70% of the time it's something small like MTU or cipher settings, but the other 30% is just hardware bottleneck or ISP throttling. People overlook that Pi isn't a beefy server and expect super speeds