The best recording level controls to my mind are simple increase/decrease buttons for two reasons-
They lock with the hold switch.
The adjustment is incremental (you can count the number of pushes and know exactly by how much you changed the gain) but usually not audible.
They take less room on the machine.
The knob can't come off by accident and roll off somewhere on the floor.
OK that's four, and the last may not apply here. But really I think level knobs are more about marketing than actual functionality. People like knobs. I know I really dislike car stereos which have buttons instead of a volume knob.
[edit- one more came to mind, the ability to adjust input gain via remote is more common with buttons]