Do you know the brand/manufacturer of the razor on top, the one with the stain? Could it be an older generation Feather? The blade profile and scales do look similar to a DX. Perhaps it is made from a grade of stainless steel that is less corrosion resistant. Or it is simply older and has been subjected to a lot more things.....maybe that is just hair dye sitting on top of the razor in the small surface grooves and not really corrosion?The shape is very similar to DX, but the material of stainless steel and the detail design seem to be different.
DX is 55g and this is 51g. The head part is a little lighter and the balance during use is different from DX.
There is no superiority or inferiority in in the balance of each model. I think it's a matter of taste.
The black discoloration is just a stain due to the fact that it was used in the salon.
Excelia is not currently sold in Japan. Other KAI straight holders are not sold to ordinary individuals.
I don't know how popular salon blade razors are in countries other than Japan, but they are widely used in Japanese barbers. There are few people who love shave, and Excelia is very popular only with barbers. It is extremely difficult to obtain. I also looked for more than half a year.
Titanium coat is a technology "PINK" used only for some blades. A blade without titanium coating is also available. The holder is irrelevant.