Not necessarily. It helps a bit on Koshkas and Ringos and quick heroes sometimes. I think better aim and prediction is better. BRB is a punishment for bad positioning, sniping, and making melee bruisers regret standing in one place too long. I'd say the power of Shatterglass+BM is better, and makes up for any extra milliseconds you might gain with a Frostbite. Often your thunderstrike or rocket leap will hit a hero first, wasting the frostbite effect before you can use your BRB.