We have 4 bounce height speakers and I've tried the system Dirac equalized with them included and not, our AVR can switch between equalizations. Again, let me emphasize I'm only interested in music, not movies. The difference isn't huge IMHO, but it does add a noticeable difference in spaciousness and feeling of being at a performance. My initial goal with going to the expense and hassle of setting up an ATMOS system was to better simulate a live music experience, and the height speakers do add to it. However, my experience is that while noticeable, they're not a big deal compared to the main horizontal speakers and going from stereo to ATMOS. OTOH, if you're interested in movies, particularly action movies, my understanding is that the height speakers are a significant improvement, and it's probably better to have them direct firing, not bounce. That's not my interest however.
As I said, my interest initially was to get closer to live performances, but what I was really surprised and very pleased by was the substantial improvement in perceived sound quality. What we both noticed immediately was how much more understandable the lyrics to songs are, then we noticed the increased localization and clarity of individual instruments in jazz groups. With a well engineered ATMOS track, it's all quite a bit better than stereo. As I said, if I accidentally have an UtraHD track mixed in with ATMOS tracks in a playlist, I notice it immediately even with the levels automatically adjusted. Unfortunately, a lot of albums will have almost all ATMOS tracks but one or two stereo tracks which is annoying. Also annoying is the poor engineering of some ATMOS albums, particularly some classical remixes.