Yes, they are extremely effective. It's one of the reasons so many "Old Schoolers" get all bent out of shape over them.
I personally do not like hunting out of mine. I'll do it if I have a small kid along or its raining. However, they really seem to screw up your field of view. They also limit mobility -- both to their weight and bulk and the time it takes to set them and break them.
As a lightweight alternative, I would suggest a 12' piece of die-cut nylap and a 50 foot length of camo camper's cord and a few clothespins. I can put up a blind in a minute or less and it weighs less than a sandwich and a coke. Just like a fancy blind, the turkey is completely fooled by all but the biggest movements you make behind the blind.