taxydual - well that proves if you own decent reference books, you should read them carefully, and not skim them, which I did initially. I now find in the section on rank insignia, 1918, a description of the braid with the following "Above the braid, a crowned metal eagle was worn. These were supplied in pairs, the eagle always flying to the rear" In my defence this is in the section for 1918, when the RAF was still using army ranks and there is no mention of cuff eagles in later sections, so I have no idea of when they went out of use in the RAF. It's obvious though that they were used in the RAAF in WW2 as shown by the picture of Sqn Ldr Blessing above.
Sorry the link didn't work for you Danny, it's just a discussion about these wound badges on another forum, and confirms what you've told us. Wound stripes were commonplace in WW1, when they took the form of a metal plate fixed with two lugs and a split pin. I think their reintroduction in WW2 was a bit of an afterthought - certainly they don't seem to have been widely worn.