Good discussion - lots of interesting ideas.
I like power tools, especially routers, I suppose that's why I came up with the idea to make nice looking comb guides with router bit profiles. I have used several comb guides, including wedge in sideways, and thin strip of wood glued into slot, even a starter strip of foundation in top bar slot. But due to my OCD like tendencies, I need the unity and symmetry of a router bit profile be cut into my top bars, and the same need drove me to select this router bit profile as one that appeared most functional for the purpose.
In no way do I believe my bees absolutely need this as much as I do.
I like my power tools.