I've had this knife for about a week now so I can't comment on edge retention, but I just did some reprofiling and wanted to share my observations on its geometry.
The distal taper is almost perfectly linear, measured 3.0mm above the heel, 2.7 at 3/4 down the spine, 2.4 at the midpoint, and 2.1 at 1/4 to the tip before thinning down. If you're into arbitrary traditions, I measured 1.1mm at 1cm from the tip, which feels usefully thin but not delicate. Doesn't quite glide horizontally through onions but performs decently. It's my first workhorse guyto, and the only similar grind I can compare to is a Mazaki 270 suji - for what it's worth, the Doi is more slender and feels well balanced, exactly what I was hoping for in a hefty convex grind. Takes some force to get through apples, but carrots aren't a problem, maybe due to the extra weight. I can hear splitting but it powers through them.
The profile was disappointingly faceted, not a continuous curve but four sections not quite blended together. Hopefully you can see what I mean with my edits to the photo below. It's subtle to the eye but very noticeable on the cutting board. I could feel a jarring thump about 3cm forward of the heel instead of the smooth satisfying curve I was hoping for. I spent 20min on a SP1500 grinding down the lumps in the edge and resharpening. Now I can see the appeal of the KS profile, but it took some work.
I didn't try to do much flattening, but I roughed up the face of the knife just to check out the grind. That revealed a few divots, about what I was expecting from a handmade knife in this price range - my Watoyama nakiri is worse tbh. Nothing some sandpaper can't fix since I'm not a kasumi polishing guy, but heads up if you are.
Out of the box the edge wasn't particularly sharp but the food release was amazing. After sharpening the food release has taken a hit. Food sticks to the lower half of the blade but the convex prevents it from climbing all the way up. I can't believe I did enough flattening to affect the grind, only about one minute on a 1500 grit stone. I wonder if sharpening to a keen edge makes cut surfaces smoother and stickier, or maybe it's the 800 grit sandpaper finish I gave it instead of the factory mirror polish (though I realize those are contradictory theories). I have no idea, food release still a mystery to me.
Edge retention remains to be seen, but the steel feels excellent on stones. I've become a big fan of blue 2 at 62-63 hrc, and if it's similar to my Watoyama I'll be very satisfied. The iron cladding is very mild, which is a welcome surprise for a Sakai knife. The core steel seems more reactive, if just barely.
Hopefully my nitpicking doesn't make it sound like I'm unhappy with this knife. Overall it's exactly what I was looking for, an authoritative workhorse to complement my delicate Watoyama nakiri. I'm loving the combination of hefty convex grind and KS profile, and there are no other knives quite like it. My Doi with custom keyaki handle weighs 212g, while the original Masamoto KS is listed as 176g on JCK and must be significant thinner (not to mention its yucky white steel with reportedly poor edge retention). The Mizuno KS in blue comes closer at 190g, but its profile looks disappointingly curvy to me, not really KS but KSish (not to mention being twice as expensive).
Tl;dr I'm very satisfied with the Doi so far. It feels like a well balanced workhorse, not too extreme but just right. The unevenness of the profile is its worst feature, but the knife has good bones and will reward the work put into it. Also, I bought mine unhandled and shouldn't diss the stock handle without trying it... but combination of angle to the spine and offset machi flush with the finger-side of the handle just looks silly and over-designed to me. There are more photos in the 'newest knife buy' thread if you want to see my semi-custom handle installation:
https://www.kitchenknifeforums.com/threads/show-your-newest-knife-buy.7655/post-762535
