If part of the idea is to teach/hear/feel arm whip, you can use a towel or a children’s plastic Jai Lai (sp?) thrower to get the same effect with probably much more safety.
I can see some benefit. I owned one for a bat many years ago. The air resistance is very real. Like swinging a bat or a arm with a parachute dragging. It does supply resistance.
I put this thing together for a neighbor, who I work with, when she told me that she would not be able to join a travel club and would have no way to pitch over the winter months. My thought was to find a way for her to keep some muscle tone so that when varsity started up in the spring she wouldn't be starting from scratch. We worked on sizing and getting it to the point where it was comfortable, then we settled on brief workout regime that would be convenient for her. She did find an 18+ team that scholarshipped her, this allowed her to practice a handful of times over the course of the 4-5 winter months. When varsity got rolling I was pleasantly surprised to see that her velocity had gone from mid 50's to the upper 50's, hitting 60 at times in the early innings. However, she also began having symptoms of thoracic outlet syndrome, this wasn't completely new for her but now it was a constant thing. I have no doubt that the use of the arm strength trainer was a major factor. She went on a stretching program and was able to control the TOS. It's no longer a big issue for her as long as she stays with the program. This past winter she did not use the trainer because of the TOS issue and she pitched about as often as she did the year before. During this varsity season, her senior year, her velocity was down several mph.