I ran a stuck one for 20,000 miles in a 216 and had no real issues. It did sputter a bit when it was real cold out if I tried to take off before the engine warmed up, but I seldom do that anyway. It didn't take long to clear up and run right. Our climate is on the mild side, so your mileage may vary, as they say.
One neat feature of the design of the fully functional one is that when you goose the gas in the cold condition, the rush of the extra exhaust pressure pushes the the flapper into the warm position momentarily to allow better driveability under acceleration.
