The Cummins VGT on the ISB is a very effective braking aide. I seldom use the air brakes until I am almost stopped, even with toad attached. It does take some practice and experience in gear selection to determine which gear to use when descending some grades. For those experienced with Cabbage Hill at Pendleton, OR...I can descend that grade in 3rd gear (MH2500) and need to use the air brakes very sparingly to bring my speed back down. Try it in 5th (overdrive) and you will have your hands full. No, the VGT is not nearly as strong in braking as some of the Jake Brakes but it is nothing to dismiss either.
'07 Winnebago Journey 34H, ISB-02, MH2500
Toad - '08 Ford Taurus X
Blue Ox, Aventa
US Gear UBS