Easier to use gadgets on a timeline
Gadgets work too differently when put on a timeline. A keyframe is easy to use. This is because you know it will be powered on when the playhead is on top of it.
Unlike the camera gadget, wiper gadget and a few other gadgets, you set a time for their transition instead of it being based on where the gadget it placed on the timeline.
This makes it harder to work with those gadgets when using timeline and I find it more accurate to keyframe those gadgets instead of putting them directly on the timeline which is more work and more complicated than it really needs to be.
It would be better if controller rumblers, wipers, camera shakers, grade effects tool and cameras act the same way keyframes do when put on a timeline where it creates a smoothing line in between so you are able to see exactly when the gadget transition will be complete instead of eyeballing the time and settings, this would be very usefull.
TAPgiles, I know how this game works, also, you can not fade, or transition a rumbler from 50% to 75% for instance, by connecting them together. If you want that you need to keyframe them to get the exact result you want, which is annoying. Same goes for cameras and shakers. If you could place 2 cameras and get that "keyframe transition line" between them, it would be 100x times easier to make cutscenes and other things instead of having to eyeball the transition time seconds every time you want a new view.
Oh also, some gadgets have fader handles on the top-left and top-right which are tied to the playhead position and power the gadget to different degrees depending on that fader line.
If you turn the transition time to 0 on those gadgets they will have no transition time and cut/instantly turn on. The keyframe has slow-power-up/down settings which work the same way as transition times. So it's not like keyframes and cameras interact differently with the timeline; they just have different default settings.
All gadgets become powered while the playhead is over them. If you have some sort of transition, that starts when that gadet becomes powered--just like when it's not on a timeline--and can extend after the gadget becomes unpowered--just like when it's not on a timeline. If those gadgets worked differently in different places it would be more confusing.
Rumblers don't have a transition time. Shakers don't either. Grade effects don't either. Not sure what you meant about those.
This is exactly why I don't use multiple cameras and transitions. I use one camera with cut-to. And keyframe its position/settings as I would anything else. I find this very easy to do.