Another trade off could be Private Relay being able to play nice with outside services. For instance I found ProtonVPN to cause issues with banking apps/websites and also with my Tesla app. Both work fine with private relay. It is also seamless to use private relay with custom encrypted DNS like NextDNS (as long as you use a profile instead of an App).
The main downside of private relay is the inability to choose a custom location to defeat geo blocks.
After going back and forth on this issue myself I’ve come to use Private Relay for every day use to protect my traffic from ISP snooping and use ProtonVPN for when I want additional VPN capabilities….like watching something available on foreign Netflix but not US Netflix.