BP remains a great mystery to me, even with the device. My cardio fitness is pretty good despite carrying a few extra pounds (I'm in the low 50s for resting heart rate), and while overnight I dip down in the 120's, I can see it shoot up based on various things like cold plunge, caffeine, exercise (during), etc. I can also see it drop temporarily (hot tub, meditation, the hours FOLLOWING intense exercise, etc).
I had many pet theories through the years - that I had white coat syndrome, that I disliked the feeling of the cuff, etc etc. But the device showed me that, no, something really is going on independent of these pseudo-causes.
BTW water retention seems to play a big role. When I did keto, which causes a big drop in water retention, my BP also went down. Strange. Supplements have an impact too.
All this to say - get the device and see for yourself, but you might find yourself in the same place I am - which is that you have much better understanding of what's going on in terms of symptoms but are still on the search for "the underlying cause" if there even is such a thing.