Channel knife? More like "out of style knife."
This is not a zester, a zester is any number of other culinary tools that is not this. The channel knife went out of style for the y-peeler 10 years back. I pretty much only use them for Vespers (long thin slice of lemon) or for quickly peeling an entire lemon when making a half dozen zests at once.
The channel knife is an atavistic tool, but I still value them.