The lifejackets the FAs use (as well as the oxygen masks and seatbelts) are "DEMO ONLY" models. They do not contain the same parts (namely the compressed O2 cylinders) that the pax versions would have. All of these things are for demonstration purposes to show pax how to wear them. It's the same idea as the dummy phones they have at a Rogers store. They're all plastic with no internal parts/screen.

There are no such thing as "better" vests for other classes. In the eyes of a regulatory authority a passenger who pays $1 is just as valuable as a passenger paying $15,000 for full fare F. Pax/infant vests are yellow, crew vests are orange. That is an international standard.