Others will know more about this, but as far as I know, the main difference is that Nashiji uses pre-laminated pieces of steel, while Maboroshi is made in-house. Inhowfar this actually translates into performance differences as far as the steel quality is concerned, opinions will vary. I have my doubts that blind testing would reveal dramatic differences, but other people might be more sensitive than me.
The Nashiji-knives I have handled tended to be somewhat slimmer than Maboroshi, which I actually preferred, but you might not. Mab is nicer since it is a more individual finish.
I would be pretty sure that as far as sharpening and care are concerned, the lines are identical.