Diffusion could potentially be more efficient for local inference. With auto-regressive models, token generation is basically one token at a time, and so is not compute intensive at all -- it's bandwidth bound. With diffusion, you always run the model on a decently sized batch of tokens, so you should be (close to) compute bound even for local inference.

If the "output quality per compute" is roughly the same for diffusion and auto-regression (is it? I have no idea...), then diffusion will be much more efficient for local inference because the same amount of compute can be packed into a much shorter time period.