It's not the putting on they really mind - that took me a few tries after they got used to me (wo)manhandling them.
So... just a few weeks actually- getting them to stick their heads in the smallish loop was the most difficult part-, and I am *no* parrotwhisperer!
They just won't stop chewing and pulling once it is in place. -> I sort of got stuck with them there...
So I went back to square one - Sunny (new to it) has to start somewhere, so the greys can join in.
(Or the other way around - sometimes I am not sure what they are up to

)
She is after a few weeks in the "I will shake it to death", "throw it all over", "stick my head in the first loop, grab the treat and then scuttle backwards as fast as I can" stage.
I am not sure if the greys are actively mocking her, but they give grand immitations of how she does it!
(they both will just let me put it on them, they don't really make a fuss or care what I do but also will not actively participate during all of it -> hence the square one for them.)
I wanted Sunny just to get chill around it first, but after seeing the greys get treats (!) for sticking their heads in a loop she insisted!
Sometimes she will take a run at it - and get herself entangled - drama and panic of course - and after being untangled and a short breather she will just try again...
(she is treats-crazy? Munchy-mania?)
I almost wanted to find someone with a really well trained aviator-savvy-parrot so they can see how it is done! I am sure it will only take them a few sessions around said bird to get it right.
Its inventing the wheel over and over again that is the difficult part (for all of us).
Maybe I should let them watch the instruction DVD's by themselves and talk it over.