Got a Gigabyte Osmium a couple of months ago and I really love it. I don't have any experience with other mechanical keyboards so can't compare to those but it is a marked change from my old G15.
The volume wheel is actually one of the reasons I went for this one as using function keys etc put me off other keyboards. It works great although just like middle mouse button clicking the mute function is easier just assigning to a macro key. The backlight wheel works as you would expect.
The only issues I have had is one of the LEDs went out after a week or so, if it was a common key I would have got it exchanged but it is the * key on the keypad so I don't even notice. The backlight also doesn't turn off on the keyboard when my PC is powered off so I need to remember to turn it off before shutting down (you can't turn it off when the PC is off), if anyone knows a solution for this let me know
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The only thing I have done in the macro software is assign audio functions (play, next, mute etc) to the macro keys (which i don't think is possible on some other keyboards macro software) so i don't have to use function keys.