[DFrantz]

You can always engage on deceleration, it just takes more driver input to use, which most folks while driving prefer not to have to think about.

 

[DFrantz]

My only concern is when we are slowing down in B mode, if the brake lights are not engaged, someone who isn't paying attention could rear end us for using it. Thoughts?

It's not a very aggressive slowdown. For myself, driving manual transmissions a good chunk of my life, it's no different than downshifting on a hill. But as a precaution, you could turn on your rear fog light, or flash it even, if it's an extended slowdown and you want to be more visible to the change.