Delta timing is not the best method for a breakout clone because it's possible for the ball to pass through objects. Fixed Rate Logic would be a better solution.
I agree. There's not much worse than a bug which only occurs on some computers, and this is exactly the sort of game where you could very easily get that. With something like this you could probably get away with fixing the frame rate at 30fps, so even very modest machines should be able to keep up.