I have not seen a bystander initiate CPR.
No.
Anything you can do to help save a life is better than nothing at all. Also, seek the help of 911 to walk you through it
EMTs will immediately step in to take over CPR, especially if the bystander is tired. Let them! It can be a very exhausting process. Help in other ways by gathering information from other bystanders or family. Everything you can do to help in a CPR emergency could help EMS and the patient.
Inefficient compressions
Have a plan, get trained, call 911 immediately, make sure the scene is safe, and begin compressions as soon as you can. If there are others around you, ask if anyone else knows CPR. You could save a life!