I had ties to both Zee and Zed-speakers growing up, but in my experience, Zee and Zed can be used somewhat interchangeably, even across the pond. This might be in order to account for names (like Z Z Top and Jay Z), puns (such as La-Z for lazy) or even ease of pronounciation - when playing CSGO, I’ve heard Americans refer to the CZ-75 as Cee-Zed-Seventy-Five, because they found it weird to switch between the cee, zee and seven sounds, but I’m not sure how common this is.