Peak flow meters are accurate if you use the same one all the time. When you switch from one to another you can get very different readings. I'm sure some are better than others. I'm probably due for a new one, as the one I have is probably 15+ years old. Ya think?
I'm another one whose GERD was creating havoc with my lungs. I had the Nissen surgery four years ago, and once my lungs had a chance to heal (about 2 and a half months) they were 100% better.