Shimano downtube cable stops

I have a frame with what I think are "flat" as opposed to concave downtube bosses:

It used to have these chunky cable stops:

Can anyone think of a reason that these Sora/Tiagras plastic jobbies would be a problem in lieu or the heavier alloy ones like the ones pictured below and above? Also where they can be picked in London or the UK?

Guaranteed to work at a lighter weight than the originals are these also:

#nerdygeekout

Don't worry - all cable stops have a round hole in them. I guess they flatten the sides of the posts because it isn't really necessary given the way the forces act. You should be fine.

I'm not worried about the holes in them.

I think the info I was given may be incorrect about flat or concave. Does flat/concave relate to the shape of the base of the unit? If so, wouldn't choosing flat be wrong as it would not sit flush with the curvature of the downtube?

"Flat" stoppers (which are modified concave stoppers) have been made for early alu and carbon frames like Alan, Vitus, TVT, Cadex, ...
These frames have shifter bosses with a large, flat base.

Either way, it doesn't really matter. If the ones in your photo dont match the frame, you can just file the plastic off to make them flat.

concave you reckon...

The concave ones have a square cutout on the underside that will fit snuggly over the boss + base and match the tube. Just like the washers/spacer things you get with downtube shifters