I was able to swap my small shoal of Armatus from feeders to smelt about 3 months ago with ease.... but I'm not a huge fan of the oily smelt stinking up my tank. I went to work for a day and had to skip a feeding, when I got home I decided to throw in some market shrimp to feed my Poly's.... two of the Armatus went for the shrimp and took them down! I thought it was a fluke and tired it a couple days later.... again they took the shrimp! Not completely convinced I tried it again today and three different Armatus have taken them willingly and took 3-4 shrimp per in a feeding! I'd say I'm pretty lucky...... 
dumb luck is still luck!
dumb luck is still luck!