All day motorcycle rides are like an all-day mediation retreat for me. Definitely feel both detached from my everyday worries but also very connected to the scenery and nature. I am a snowboarder and former surfer/skater.
I do track days but the best comparison to what I feel snowboarding would be nice smooth windy roads in nature. The fact is most the noise riding a Zero or an ICE bike comes from the wind, not the engine. I also have a Ninja 400 and that bike will ride circles around my Zero on a windy road.
But I have been repeatedly disappointed at my FitBit readings after riding all day, haha! It will raise your heart rate more than sitting in front of a computer, but below even casual walking. With a resting heart rate of 60, my last ride averaged a HR of about 80, with a high of 103. Walking, for example, will raise my heart rate to 100-110 consistently. But FitBit is reporting over 1 hour in my "Fat Burning" zone so that is something!
But unless you live with great scenery nearby (in the range of an electric bike), and you have the time to ride more than an hour, maybe what you want is an ICE bike?