"High weight" as a con. Sigh, another fail review. Time and time again, gaming mouse reviewers always note that as a bad thing and it all stems to marketing. Pushing lighter every chance they get. "Lighter is better!"
Lighter is not better, lighter = carpel tunnel. There are plenty of studies out that show you do not want light mice. Lighter requires more muscle movement than heavy because our muscles are constantly having to keep it maintained. In repetitive motion under gaming environments, you want a mouse that is either adjustable or something you can add a weight to. A little weight is good. But what do reviews always say,"lighter is better!" I've lost count of how many people I've had to educate in the last 20 years or so. People who were sold on the idea of light and then discovered how much of a lie it was after I showed them. No more wrist braces!
That said, 604 looks like a pain internally compared to the 602. As a 602 owner, I see more reason to buy another 602 than a 604.