I use one on my straights. I like it a lot. I don't find it produces a "too sharp" edge. My results are always a smooth and keen edge (as long as I've done the proper work on lower grits).
For me this hone is better than my experience wih chrome oxide, which tends to remove some of the sharpness from an edge. That's a different thread though.
Totally agree about the diminishing returns. I've got a Shapton 16k and a paddle strop w/ ChromOx. Gives me incredible edges. Doubt I'll ever drop $250 just to find out if the 30k is worth it.
IMHO if you're tuned in enough to notice a difference, you're an experienced straight shaver and getting comfortable and close shaves regardless. It's not worth the $250.
A few hours of practice at honing will be worth far more to anyone than an expensive stone (which, icidentally, is useless unless you know how to use it right).