The distress calls are the same, since all they do is mimic animals in distress. The howlers that I have seen and or read about used thicker reeds. But I never played any of them or heard any of them played by someone that I would consider an expert. Rich Cronk sold some before he passed on, I saw pictures of one, but never heard it or played it myself. Another callmaker that I cannot think of his name but his last name starts with an H, has or had some, but no clue if any are available.
There are a few of the commercial calls on the market, the one by E.L.K. I have seen, but I have no clue as to if it is any good or just sales item. I really don't believe there has been enough hunting and experience with wolf calls for most hunters to have a clue if they have a good howler or not, I know I don't.
Marvin