I think they are complementary, since one is about browser site isolation, and one is about process isolation on the computer.
Using temporary containers, multi-account containers, site isolation, along with a number of other privacy/security addons such as Umatrix, LocalCDN, and many others, I have not noticed any slowdown.
So far it seems to work fine for me too. Can you share you list of security/privacy addons? I've used Umatrix but never heard of LocalCDN. Was wondering what other gems you may have found.
Here is a complete list of security/privacy addons I am using, a small number of which I have disabled, as I regularly toggle them depending on what I am doing at the time
