I used to have a mare who couldnt stand metal and had her in happy mouth all the time, she did chew them though so we got through them v quickly, now i prefer nathe bits as they are softer and a kinder shape for the horses mouth and tend not to burn like happy mouth can!!
Got one, my first, only used it a few trimes. It doesn't smell appley to me but seems very interesting to her! She does seem to chew it a lot and I'm not sure how much I want to encourage that - she has a nice mouth alrady and I don't want her to start getting preoccupied with chewing!
I also have a nathe and in terms of quality - and price - the nathe is better, and MUCH more expensive. I noticed when I got my HM bit that it's moulded and there is a raised seam which could bother a sensitive horse - ideally I'd have taken a nail file to it.
The HM bits just feel like plastic, the nathe are more of a rubbery feel. My mare doesn't like metal bits at all so I will have to go HM or nathe all the way for her. I have a stright-bar Nathe and double-joint HM, I think the ideal bit would be a double-joint Nathe, I will probably end up getting one but it will cost a bit so I'll have to wait!
When I bought my boy at 4 years old he had been with an inexperienced rider for about 6 months and I couldn't get the metal bit anywhere near him. Moved onto a happy mouth double jointed loose ring snaffle and he was alot better, he hunts, xc and sj in it, he is 8 now. My friend put her horse in one and it got chewed to bits. My boy is very sensitive in his mouth and so this suits him down to the ground.
My horse was in a happy mouth bit which I had to replace a few times because he kept chewing it, I was riding him one day and he reared up and went over and landed on top of me and put me in hospital with a broken back, after investigation (vet, dentist, back etc) it came down to a sharp point on the bit that he had chewed whilst riding him.
Not sure I would use one again after that as the bit was fine when I started riding him that day.....
I had to take my mare out of hers as it burned the corners of her mouth and made her very distrustful of the bit as a result. Her mouth was a mess and took months to heal, it was awful.
I had one for my mare, she seemed to go very well in it, but when I took her bridle off a few weeks ago I noticed she had chewed it quite badly and it was very sharp in places, wouldn't mind but I hadn't used it very often, I will not be buying another one.