Rifle nades are one of the worst grenades in the game. Takes ages to throw so even a brain-dead could dodge it and 30 muni/nade......and also costs extra mp and fuel to unlock it, it's not worth it atm.
This used to be true, but I feel like they improved this at some point. I feel like they launch much faster than molotovs now - there doesn't seem to be a big wind up any more.
EDIT - I do wish that AT 'nades were unlocked at the same time. Waiting for vet 1 for AT nades is a little unfortunate. Plus, give Rifles AT nades at the game open, they could scare off or kill Kubels more readily.