i have experience with both tojiro dp and tosagata style knives
tosa knives are:
as for the handles handles are ho wood (magnolia family) and plastic ferrule construction, cheap but can be easily replaced when they either break or just wanna rehandle them. replacement handles are sold on ebay for a few bucks. i dip my handles in mineral oil every few months, seems to work fine for me. i love the grip that i get from the naked ho wood. real grippy even when wet. seems to be quite water absorbent. dipping it in mineral oil helps the tang from rusting out. some japanese cooks even take out the handles when cleaning it, they take it out and leave the tang and handle to dry completely before putting it back on. since they're friction fit, it's really easy to do.
i think the steel they use is either white #3 or some form of yellow paper steel. those guys don't really say anything about the kind of steel that they use. as we all know, they're kurouchi. coated with a soft iron to protect the knife from rusting and whatever.
reactivity with certain foods, of course they're reactive. they're carbon. just as reactive as any of my carbon knives. the most reactive carbon knife i have is my left handed misono swedish steel hankotsu. as for the carbon steel that's used on tosa style knives, they're somewhere in between my suisin hc gyuto (thought to be sk4) and my misono swedish steel. so it's slightly more reactive than say maybe blue steel or even my vintage old hickory which is 1095.
as for the hardness, they're comparable to any of my japanese knives which is around 59-60rc. at least by feel from sharpening and use.
ease of sharpening, well, it's carbon. stupid easy to sharpen. really thin behind the edge, takes a great edge, feels really fine when sharpening, if i don't clean up my stones the stones end up getting rust spots, i get orange spots on my suehiro rika 5k if i don't rinse it off. doesn't happen much with my other carbons. i take it up to the suehiro rika 5k, i don't have anything higher than this that's got a grit rating. i have a few natural stones for honing and other stuff. it can't take a great edge from those. but with natural stones your mileage varies.
for edge holding, for home use, it does decently well. i'm used to having fresh edges all the time. with continuous daily use, it holds on to the edge for around a week or so. it's a pleasure to use as it's easy to sharpen and to cut with. i love the fact that the knife is really light and it doesn't take much force to make any cuts as it slices through food.
dirt cheap, gets sharp fast.
but then, since there are a lot of tosa knife makers out there, since tosa is a place and tosagata is literally translated as tosa style or tosa type.... your mileage may vary.
the ones i have are pretty good. bought mine on ebay. they're branded as ryouma. 20 something bucks plus shipping. pretty happy with them. i have two. lol.
btw, i'm left handed and it is righty biased. but it doesn't bother me much, if at all.
