My thinking is that one would be best to defer any deferrable comb-building for as long as possible (so that it could then be done by a strong colony).
Thus the idea would be to keep the nuc's original comb in use until (at least) the rest of the box had been colonised.
So any part-solid-raised-floor bodge could be in situ for months rather than weeks...
The advantage of the frame extensions looks to me that they could be left even until the following year(s) to swap out. There should be less pressure to remove them, no floor-block needing to be removed and reduced from 5-frame to 4-frame size (and so on), less bee effort wasted on brace comb, etc and so I'd expect the nuc to be more productive, more quickly, using the extensions.
At £15 for (10) extensions+foundation, they look as though they ought to be worthwhile for the already-drawn frames of a nuc (or two), in reducing beek hassle and colony growth disruption.
I'm sure there are better ways for shifting strong colonies over, but if those extensions have any valuable function (maybe debatable!) then it strikes me that it would be for use with nucs.
