Tied in the larger size range these would probably be killer around mid-May in the Merrimack River when there are tons of river herring present (alewife and bluebacks). Heck in any coastal river that supports runs of stripers and herring it would work.
I tried to tie a larger fly to imitate them last year, but failed badly (too heavy to cast when water logged), this looks like the ticket. In the fall tied towards the small end of the spectrum (~3") it would pass very nicely for the outmigrating juvenile herring.
With the larger sized pattern - Have you ever tied it using a tandem hooks? The reason for the question is that this pattern would probably work just as well for bluefish. Stripers in my experience take everything down headfirst (99% of the time), but bluefish, at least when they are small, will attack larger prey from the rear and bite it in two - then other fish snap it up, or they come back to finish off the job. Having a rear hook, even though it is a headache, may result in some additional hookups instead of bumps. Just a thought.