I think the main benefit of the aviator harness is that it doesn't require buckles. Also, it may not be something that you care about, but the design allows parrots to fly while wearing it which many other harnesses do not facilitates well.
For Kili, the #1 reward for cooperation for harness removal is freedom. Getting the darned thing off is negatively reinforcing in itself so generally once they are aware of the removal procedure, they do not mind as much.
Now I do have similar problems as you mentioned with Truman. I think the biggest problem is that they don't make a Cape Parrot size harness. You're forced to choose between one that is a tad too small or one that is a tad too big. Cape Parrot is just an odd size like that, kind of somewhere between the TAG/Galah size and the CAG/Amazon size.
While Truman was a baby, he didn't resist the harness much but after a winter hiatus and a little more maturity, he has been showing greater stress over the harness. Before I used to just stick it on him and that's it but now before the summer season hits in full bloom, I began practicing harness donning as my main training focus. I just followed the same exact steps that I outlined for
Kili's harness article. In fact she has gotten rusty over the course of the winter and was a bit annoying about putting it on so I retrained her again as well. After about 2 treats for sticking her head in, she was as good as before so it was barely any work with her. For Truman on the other hand I practiced for several days (pretty much following the Kili 3 day plan exactly).
I started with the holding harness material closer and closer desensitization, then touching, then draping, then sticking on head (but with big area, not collar), and then finally with collar. He's not as good as Kili by any means but when he gets into the training he will stick his head in himself and help it slip onward. Then I put the harness on completely and give him an almond. With an almond he forgets about the harness entirely and I let him eat it to reinforce how great it is to be enharnessed. Now having used the technique on two parrots I am absolutely convinced that the method I outlined in the
harness article works great! It doesn't even take that long to do. Three days is really a realistic span of time for an already tame bird (that might have gotten off on the wrong foot with the harness). After putting the collar on and off of Truman like this a couple dozen times in the course of 3 days, he got less upset about the difficulty of taking it off. He has also learned to remain more still when I pull it off rather than to fidget cause then I have less trouble taking it off and it comes off quicker.
Your husband just has to follow the harness taming program step by step (as long as it takes, gotta adjust timing to the bird). You gotta keep practicing, negatively, and positively reinforcing this process until the bird puts the harness on willingly. If the harness removal process is too unpleasant, it won't be long till the bird viciously prevents you from putting it on in the first place. This is why it is very important to make the proper harness training up front. But it should make you feel better that both of my parrots have at some point had a TERRIBLE experience with the harness but with my training method overcome the fear and don the harness willingly. The only way you can know the parrot is ok with wearing the harness and won't fight or hold it against you, is by letting it put the collar on itself.