In asking if an intruder type fly would be effective for smallmouth's.
I believe they could be useful as the one hook design.
All fish have territories that they protect from the encroachment of others. Rainbow trout, steelhead, and Chinook salmon can be extremely territorial.
An Intruder fly is meant to trigger aggression when invading, or intruding into the territory of a sport fish, thus eliciting a strike response.
The most productive “Intruder” fly patterns trigger the fight response without triggering a flee response by scaring the fish away from its territory.
These types of flies become even more productive if they also mimic something that the fish has been feeding on, so that the “defend” response is combined with a “kill” response.
The Intruder usually uses only one hook but tandems can be tied.
A hook is mounted to the rear of the fly hence the name given to the hook is a trailer.
The Intruder has a large profile and creates lots of movement without using a long hook.
Advantage: It is tied so that the hook can be changed out for a new one, a different sized one or a different style.
Single hook attachment summary: See articles for details
1. The fly is tied to a shank with a large wire loop or leader loop at it's end. The hook is attached with a loop to loop connection.
2. The fly is tied to a shank with a small wire loop or leader loop at it's end. A tippet is then passed thru the shanks front eye, down along the fly, and thru the small loop. The hook is then tied to the tippet (a junction tube is optional).
3. The fly is tied as a tube fly.