While I absolutely love the idea of an advanced jetpack (I sacrifice armor to use jetpack 24/7), I also agree that the toggle isn't good.
It's not a bad idea to have a toggle, but its "on" mode should behave like the normal jetpack - having it drain power and not be responsive defeats the purpose of using it vs. other flight options. I also firmly believe that I will die due to this feature if I ever turn it off - which I'll be forced to do, due to the power drain - because I'll forget and jump off a cliff. This happens just because of my forgetting to charge or put on my jetpack, so having a button for it will only speed up my suicides.
I also use the jetpack to escape situations like falling, being approached by a creeper, ending up in lava.. these require reaction time, which can't happen if you have to toggle modes to fly.