I've been on one short first aid course.
I am most certainly not an expert.
The instructor did recommend using duct tape.
I've asked him if he can provide any clinical trials of duct tape for first aid use, and no, he cannot, merely what has worked for emergency medical teams, civil and military.
I'm not in the least bit emotive about the issue, but I am very much a pragmatist; "if it's stupid and it works, it isn't stupid".
> When actually all first aid instructors should be teaching the same protocols.
Well, there's first aid and there's first aid, and they're not always the same, so I'm not surprised that different things are being taught, depending on the intended deployed environment. What is applicable in an office environment with a large, well-stocked first aid kit will be different from what is applicable in the wilds with a more limited (due to practicalities of carrying the thing) FAK. A good example being CPR advice; urban FA 'best practice' is now not to breathe for the casualty (hence the BHF Vinny Jones advert "you only kiss your missus on the lips"), whereas remote FA advice is to continue breathing for the casualty, since it will be longer than the 8 minute target for an ambulance and paramedics to arrive. A recent TV programme allowed two military medics to compare their small, personal FAKs, and they were different (and carried things unlikely to be required in a walker's FAK, such as tourniquet devices). And a lot smaller than the large medic's more comprehensive backpack.
And there's also the issue that even things that are clinically tested and found to have adverse reactions are still used; drug side-effects, allergies to latex and zinc oxide, and even micropore tape. And yet we knowingly use these items, and even suggest them as 'best practice'.
I'd actually suggest that blister treatment isn't really first aid at all, but palliative treatment... In most cases, blister treatment is intended to allow someone to continue their activity, whereas the 'best practice medical advice' would be to stop whatever it is that's causing the damage; i.e. cease the activity. "Doctor, it hurts when I <insert activity here>" "Well, stop doing it, then..."