I've heard they are supposed to be quite good for some people. I wonder if they would do anything that blowing up balloons wouldn't do? (This is something I can do better than most)

It seemed to be designed to make normal breathing harder while using it, rather than have huge exhalations at irregular intervals, so I imagine it's just a different form of training - perhaps similar to wearing arm and ankle weights while walking around rather than doing weight training.

One thing that blowing up balloons won't do is to have much effect on the muscles that inflate your lungs, which seem (in my case) to be the weaker ones anyway.

How about learning to play a wind instrument?