This is some info I was sent by an Australian retailer who sometimes carries Shigefusa's, it's an interesting read
Shigefusa decided to leave the famous Iwasaki razor upon Iwasaki-san's suggestion to introduce to the users (mainly the pro chefs back then) that there is a much superior option to Honyaki for Yanagi knives, which is the Kitaeji.
So their Kasumi yanagi is, in fact, not their intended product (that's why they don't go all out on Kasumi model's polishing, and don't engrave the mei either, only stamp, but that's more to keep the price affordable, not trying to slack or anything), but since there are many people who ask for them, they are complying. Until I started selling to the western world, I didn't even know Shigefusa made non-Kitaeji knives! So to me Shigefusa used to mean Kitaeji.
Honyaki was considered to be superior to the Kasumi knives for single bevel thinner knives' construction, because they don't warp (so thick ones like deba, or double bevel don't matter.) Kasumi yanagi, no matter how expensive (even Shigefusa or Heiji), will start to warp (usually after 3 to 5 years of production) due to the tension difference between the hagane and jigane, but as Honyaki is one piece, it doesn't warp.
Altho it is extremely easy to fix this warp (a kindy can fix it...), because all you need to do is manually bend, blade overhanging from the table edge, not too many chefs know this, and some are too scared to do it even if they knew, so there was a demand for non warping yanagis, and hence Honyaki was introduced. (Note to Ivan: Do you play golf at all? If you do, do you know anything about lie angle adjustment of forged irons, which is done by manual bending? Fixing bent yanagi is as easy, well, its easier since you dont need any machine!)
BUT honyakis are expensive, very fragile (if you drop it or bang it against the sink wall when washing, it could snap right in half even! If not, it's tempered too much, so the edge will not be as sharp nor long lasting), and difficult to grind, and cannot be used up all the way to the spine (you can use any knives as petty once the blade length goes shorter than 165mm, all you need to do is get a petty handle and re-attach. If you will use up a Shigefusa, Heiji or Tsukasa knife to such length, I will get the handle in and reform the blade shape to a perfect petty! That would be my honour), so Shigefusa upon his masters' suggestion, i.e. Iwasaki-san and Nagashima-san the sword smith (he is the one who instructed how to forge Tamahagane razors to Iwasaki-san, as well as instructing how to forge Katanas when Iwasaki-san obtained his national license since his father, Dr. Kousuke who was a Katana specialist at Tokyo Uni, has passed by then), he set out to introduce his Kitaeji knives, which doesn't warp.
I've owned a number of shigs, both kasumi & kitaeji.
Fit and finish is always great, the polish on the kitaeji is at a whole other level, the hand engraved kanji on the single bevel kitaejis is a nice touch but doesn't affect performance. All have been very comfortable nicely rounded & polished spine & choils.
As far as cutting performance goes (for Gyuto) I have seen some variation within the same lines, the best performers for my preferences have been a Kitaeji Gyuto, and a western Kasumi. But others preferences may vary.
Wedging I've never had an issue, but really avoiding wedging comes down to maintenance by the owner, shigefusa do have a relatively thick spine, so if not properly thinned & maintained wedging will become a problem.
I have never had a problem with reactivity, and can't say I noticed a big difference between the two lines. Like any iron clad blade, if you wipe consistently you shouldn't have an issue.
Edge retention is pretty similar, kitaeji has slightly better than the Kasumi, it's not the best, but I have pretty high standards for edge retention ( I've been spoiled by makers like Devin, Bill Burke & Marko)
