Or maybe you could use angle section. I did, on one of my Dartingtons. Just need to make sure that bee space is upheld or they might fill small holes with very sticky propolis.
I simply run the electric planer along the length if it needs reducing. The router table would likely be a slightly better route (with appropriate precautions) and I could easily rebate lengths of PSE strips if I wanted (hardly worth the trouble of setting up!).
Flaming plastic, for spring cleaning, is not recommended and removal is often fatal to the runner, so plastic is possibly a less user-friendly option both from the 'eco' and practical angles.
Type of metal? Stainless steel is likely best option but not cheapest. Bees won't mind.
Slip into a slot, or screw/nail on the side? Now there is another dilema. Ho, hum, decisions, decisions....
hi, until recently I used the galvanised runners from thornes, but if you use acetic acid to sterilise brood boxes and frames the runners will corrode and rust so I have started using stainless steel strips, no angles, just like a ruler and can be set/fitted how you like, which helps on badly made brood boxes.