I think you may need to reassess your opinion of him: "someone with great knowledge". Do you honestly think that could be true? (CO2 issue) Can you imagine the liability issues if that would be the case?
The only issues that I am aware of is that periodically it may be good to replace the arming mechanism and to test the pfd. Also it's best not to leave the pfd in a high humidity area when not being used on your boat. I always take mine home and keep it inside my house. (might be a good idea not to leave it in a hot car either)
I just had no idea. Thanks for your helpful comment.