Long answer - I had one for my pony and it seemed OK. Then I had to take him to something that I couldn’t use the Stubben for; realising the evening before I didn’t have another bridle I had to go through all the bits and pieces in my tack room and cobble a bridle together. He went so much better in the traditional shaped cobbled together bridle I never went back to the Stubben. I did have a bridle fitter out to get him a replacement bridle, properly measured and her view was that unless properly measured and fitted individually anatomical bridles were no better than traditional.
Or maybe my pony is just a cheapskate who doesn’t appreciate nice things!