I only had one emergency application where if it had not been for the brake buddy, I think I could have had a major accident on highway 101 just going into Los Angeles. I applied the air brakes all the way down and I was surprised how fast the air brakes with the assists from the brake buddy stopped the coach. Now we are talking about 34K lbs total.
So I can say that in an emergency application the brake buddy does engage, but if you just come to a light slowing down gradually, I do not believe the brake buddy engages.