I'm making good progress with n-back exercises. Today, I averaged 4-back. Now, 2-back is way too easy and 3-back is nearly as effortless. The image above is my estimation of future progress. I expect to reach 5-back before my 40th session.
As for practical benefits, I can't yet say. My memory does seem better, but I'm not sure why that would be a short-term effect of improved working memory.