in practical use I can set it with my outboard finger wrapped on the TM.
Easily done with one hand.
It's almost second nature after a few tries.
As your question you can engage it before throttle back, but I leave it off, get to freeway/speed, and then with pinky finger on the TM it's just a simple twist.
When you intall it there is a progression that you do to set it up.
there are 4 washer(spacers) that you trade out and in until the TM is at the edge if engagement (but off). It doesn't take much to partially engage and then if you are on long range freeway you can set it "hard".
It is merely a friction tension of the spacers that "holds" the throttle.
I restate, it isn't really for use in the city blocks. I like it.