You just don't do it in an adversarial way at a public gathering. Based on a few comments I got from guys who were listening to Col, a certain "Rebreather World Member not from Oz" didn't score any points at the presentation for public courtesy. Praise in public, and criticize in private. If there are constructive comments to make, especially on a trials rig, it's probably best to note them, and send a letter or email to discuss. Just a little plain courtesy goes a long way.

Dave