Good versus bad exercises, it's all about finding an exercise that provides resistance safely throughout the rom, from full extension to complete contraction.
if you are (your shoulder girdle) able to perform a BTN press like any exercise without any tension and compression of tissue and tendon around the joint, then it's a good exercise, it does stimulate posterior deltoid as opposed to the regular press.
But more often than not with the BTN press there is impingement, you can test this by moving the upper arm through the movement, compared to the standard variation, you will feel the difference, if you don't you have the green light.
its true that the BTN hits the post delt, but if you can't do this movement safely, there are lots of pulling movements you'll be doing anyway, so no big issue there.
ALL exercises are GOOD if you know how the movement effects the targeted muscle, there are some exercises where you might need to slightly change the path due to your bone shape and mechanics, I reckon that's ok we are not RIGID machines.