Well on my bike I'm wanting to keep a screwdriver and I'd likely need 8 bits so would like storage in the handle.
I need t20,t25,t40, slotted, ph2, ph3, micro Phillips and likely another small torx.
So a off the shelf unit won't work. Nor do I want some crap that breaks.
Also may consider a pocket knife or other tool that acts as bit holder.
Also any reccomened brands.
At the moment I carry a kingchrome driver and there 30 or so bit kit.
Have you considered a bike multi-tool?
Crank Brothers and Topeak are good brands.