@Xiaofei I've been using the Z for a couple years without a single problem.
I will agree that the scroll wheel, compared to my travel mouse, the Logitech MX Master 3, is weak. The MX has an amazing scroll wheel. But, I've never had any issue with it not working or the middle button clicking just fine.
In actual gaming, I rarely use the middle mouse button though. In general, clicking a wheel isn't a great experience on any mouse. So that quickly becomes one of the last buttons I want to bind to anything. Some mice I've used in the past had rocker button (push the scroll to the sides) and those I did find useful. More useful than a downward click on a wheel.
The Z isn't perfect.
I'd love to see a Z v2 that takes some ideas from MadCatz in the shell design from adjustability. (Warning: MadCatz quality has got to be the worst of any mouse I have ever owned in the past). A future version with a very precise scroll wheel like Logitech would be awesome plus extra if it has a similar electronic switch from stepped to ultra smooth (Again, MX Master 3 for an example of excellent).
I am a crazy person and would love one more button on the 3rd finger rest (facing down). There are some buttons that are very situational (like a lift on the right mid-button). In the high-heat gaming situation, another easy press would be nice. I would probably use it as a "shift" button in many cases too which would just take all my other buttons and double their use.
And, well, a gaming quality wireless mode. Going back to wired should still be available - but wireless would be amazing.
Oh - last, the LED in the logo needs to be lowered or something. It actually generates heat on the user's palm. Maybe just lighting in a different area. I just turn my logo lighting off so it's not an issue. For those who want that lighting though, it is a very small issue.
So far no mouse is perfect to me. The Z has been so great that I have a second unopened one for a "just in case".