Good question. I'm getting an 80ms ping (compared to my usual 10-12ms ping) and my download speed is reduced by half (180mbps compared to 350-360mbps) on my MacBook Pro.In which country will the relay be based ? When I am in Europe, will the relay be in Europe or will it be in USA.
On my iPhone, my Ping is around 35ms and the speed is alright, but still not as fast as without the private relay feature.
Also, I don't know if its just my phone but sometimes the websites take forever to load. Once, the private relay feature is set to trackers only in the Settings (or turned off completely), it's all good again. Might be either overloaded or in a different region, I'm not sure.
But to get back to your question, I believe it's designed to use a private relay that's near you.