Finally, something I can contribute to. I come from the knife world, woodworking being a new and still developing interest for me. Cooking, and Japanese knives, have been a long time passion.
I've not purchased knives from Iida, but I have used knives from Inotada Hamono that he sells (ironically, I happen to be selling one at the moment, not to plug). I'd have no reservation recommending them. Craftsmanship is exceptional, fit and finish are as good as could be expected.
As far as honyaki vs. kasumi goes, there are some small but significant differences. You're right to suggest that sharpening honyaki is more difficult. Indeed, it can be much more difficult, as honyaki are often hardened a few points higher than kasumi blades. Not only are you sharpening more hard steel, you're sharpening harder hard steel. The advantage of an entirely hagane blade is that it can have a much longer service life, as there is no chance of running out of hard steel (at least until the hamon is reached, but that is typically high up on the blade). Now, the average user will probably never wear out their kasumi blade, but in a professional setting that can happen in the space of a few years. A honyaki blade has the potential to last considerably longer.
As a result of higher hardness, edge retention tends to be longer with honyaki, though of course at the expense of toughness. Breaking is a very real possibility, both during use and manufacture. There is always a chance of breakage during the quench and subsequent straightening. It is said that even the best makers only achieve a one in three ratio of successful honyaki blades. That might be apocryphal, but it does speak to the difficulty of manufacture. That difficulty is also one reason why there is such a gulf in price between kasumi and honyaki blades. A honyaki knife tends to be a showcase for the best work a blade smith can do.
Besides edge retention, honyaki also feel different in use than kasumi knives. Honyaki feel crisp in the cut and telegraph what the edge is doing, where kasumi can feel damped. It's a small difference, to be sure, but it's one that experienced cooks appreciate.
I'd recommend that anyone interested in knives check out
http://www.kitchenknifeforums.com. There's a real dearth of good information about knives online, and Kitchen Knife Forums is the best community there is for serious knife talk. I can post some other links that might help if anyone is interested.
I hope this helps someone. Let me know if there's anything else I can talk about.
