Might be OK since it is from progressive industries. I do know I have had issues with the small cheap "pucktype" 30A to 110V melting. I have never had issues with a quality dog bone type. I assume the heat build up in certain cases due to the connections being so close together can be an issue.
Although I have never seen a 30A to 50A puck style. I use the bog bone type all the time in the summer as our camper now has two 30A style hookups. I use both the campground 30A and 50A plugs. But that is so I can run 2 ACs on a 30A trailer.
Maybe someone else will chime in but the biggest potential issue I see is two connections with a couple of inches of each other could be problematic. Heat build up? Personally I would not use one but I again know no one that has used one.