Thats a fair point. However as a Flt Lt, I had the option of buying a metre of braid for a couple of quid, and making my own rank (unbacked) rank slides. Simple, cheap, and useable in any forms of dress.
Now, because of the embroidery, if I want spare sets we have to pay out about £5 per pair. If we don't, we will have to wear blue backed sliders with greens, which looks gash.
Given that DPM/MTP is now required dress during fieldcraft and skill at arms, I don't think it would be too much to ask to find the money for an extra set per person - OG backed sliders would be better than nothing!