I have taken plenty with simple steel blunts and normal fletchings. They don't penetrate the hide, but they take em down nice and quick if you hit the spine or head.
I also have used an adder behind a field point, I prefer them to the blunts. I had some penetration issues because I was shooting a very dense spiral flu flu 15 yards up into a tree, and by the time it got there it only stuck the 275gr field point into the squirrel. This knocked him outta the tree, but he ran back up so I shot him again, this time in the head. That did the trick. The point of the story is use reasonably short (3.5'') 6 fletch fluflus with adders. If you get full penetration with them they are devastating. Point in case is the time I took two birds with my 6 fletch flu flus. One was with a field point, one was with an adder. The field point passed thu cleanly, and the bird flew off (found it later though). The only reason I knew I hit it was the mess on the arrow. When I nailed the next one with an adder there was a poof of feathers, the bird got knocked back 10 yards and was done before it hit the ground. Shot placement was identical on both.
Broadheads work really well too.