I just took a CPR class (starting nursing school in a few days!!) and I wanted to get a couple more face shields to carry in the car, my purse, etc. in case anyone ever needs help when I'm out and about. I was trained with the plastic shield with O2 inlet, but noticed the vinyl ones are a lot cheaper and more portable. Does anyone have input about the vinyl ones? How do they work, and are they very effective? How does it stay on the face and make a seal?If you recommend the bigger shields, do you know where I can get one or two that are not expensive? They are about $5 on-line that I can find but the shipping is more than $5 and it's not worth it. Thanks!