These joints are plenty strong and work great in the applications where they've been used. Usually that has been "foam build up" or cloth covering.

It should be noted that I've never put my armatures into a cast foam puppet model. It's hard to tell if they would be tight enough to stay in position against the resistance of the foam. Not to mention that I have no idea how the different metals would react to a cast foam covering. Other armature builders have detailed construction methods for cast foam puppets that have a proven history. I would follow their techniques if you plan to do foam casting.