well admin you said it all. but here is my 2 cents. a bag valve mask will be too cumbersome in the time of need and will only hinder your efforts since you cant hold the mask in place. so stick with the shield. the O2 is not necessary since it will take up time that you could be doing compressions. i take it you are in a rural area and are worried that you wont get an ambulance fast. just keep in mind your CPR and dont forget that after your first 2 mins call 911 since we do have more stuff available.

good luck...
CJ