That aspect of it isn`t risk and reward in a positive sense, it`s just a random annoyance. It`s as if you decide to play your cards in a game of poker and they change into different ones when you put them on the table. You have to know what is going to happen for your assesment of the risk to be meaningful, and sometimes the BR just doesn`t work, or it works late so you don`t get your boost, although this is something less of a problem in Pulse than Pure. There is good risk and reward in the game, particularly through the absorb system where you sometimes have to gamble on using a weapon or taking the energy. I guess there is risk and reward if you`re on your last pixels of energy and need a BR to win the race, but the negative points of Barrel Rolling outweigh this, imo.
I don`t see why you shouldn`t start a "Ten things I hate about Wipeout 3" thread if you want to. I could post a couple, but would be hard pressed to get to ten.