BB, tough one. I've worn out a course DMT stone in the last year, but it's stayed perfectly flat the whole time. An arkansas stone would have dished slightly from the abuse, but could be flattened again (with quite a bit of work).
The diamonds cut faster and are more consistent than the typical Arkansas stone. Ron doesn't sell the typical Arkansas stone though and it's safe to take him on his word that these are some of the best out there.
You'll get a a finer hone with the Arkansas (based on grit size alone) but with the natural stones you also get the grit breaking down further to smaller sizes, giving a finer hone.
I've been using the DMT stones on knives only. Anything that I really want to hone I go to natural stones, though I'm impressed with some of the ceramic stones that are out there now - cut like a diamond, work like an Arkansas.