I ordered a starter set last spring and as soon as I got the package open I started practicing with them. It was really rough at first but within a couple of days I was making pretty good consistent howls, barks, and PD. My idea was I wanted a howler I could pop in and leave in while I was using my hand calls and it works fairly well. I have no real issues with volume, its not as loud as my horn howler but I think its close. I'd suspect there is a difference in perceived sound volume coming from inside the mouth with a diaphragm as opposed to sound coming from the end of a 7" horn.
Something else to consider is that we sometimes get caught up in what "we" think sounds best or realistic and forget that we are broadcasting a sound that portrays a wild animal to other wild animals to trigger a response. Is it not more important how they perceive the sound than we do? Just food for thought.