I purchased a lowerlung two years ago and used it religiously for the next year. At first I noticed an improvement in my playing. As I gradually increased the resistance dial I noticed some bad habits creeping into my trumpet playing...small air pockets would build up under my upper lip between the mouthpiece and nose.
I believe this is a result over blowing caused by the powerlung. It is a great tool for strengthening the muscles required for inhale and exhale...however the amount of effort required for the exhale does not match that of the trumpet. The bore size of the powerlung and the bore size of a mouthpiece are COMPLETELY different. I would encourage people to compare the powerlung mouthpiece and a trumpet moutpiece before ever trying out the device. The center of the blow is actually blocked on the powerlung forcing you to blow around it. If anything this is where I think that the greatest intensity of air speed should be directed.
Personally I prefer the breathing excercises addressed in the Stamp book. If you are looking to increase your air speed on the exhale, try the excercise where you "blow great gusts of air" into the leadpipe. This has the same benefit of a powerlung and seems to help me to focus my air stream a little better. It'll also save you $80.