I use zx mapped on my belkin n52te but for very hard streams I also use the left mouse button I mapped left of the z on the same n52te I also mapped right mouse click but I never used it I tried playing with only the mouse the first time I played osu! but I found it hindering the movement of my mouse so I started using the keyboard instead I could use more keys then than the two osu! allows now.
I use mouse only, except where that's impossible in places (Yes, insane mode for Trans-Siberian Orchestra - Wizards in Winter, I'm talking to you!)
I tried z/x, but it just puts me off and makes me fail, plus, I play better using my left hand as support by keeping it close to my mouse (dunno why... maybe cos I'm left handed... I either keep it close or on the WASD keys, which is kinda pointless for Osu, but it just feels right)
I don't want to hurt, or annoy, or get in the way... please tell me if I am doing either.