Reading the page you linked to:

3) Are there times when I should use conventional CPR with breaths?

Yes. There are many medical emergencies that cause a person to be unresponsive and to stop breathing normally. In those emergencies, conventional CPR that includes mouth-to-mouth breathing may provide more benefit than Hands-Only CPR. The American Heart Association recommends CPR with a combination of breaths and compressions for:
* All infants (up to age 1)
* Children (up to puberty)
* Anyone found already unconscious and not breathing normally
* Any victims of drowning, drug overdose, collapse due to breathing problems, or prolonged cardiac arrest

6) Is Hands-Only CPR as effective as conventional CPR?
Any attempt at CPR is better than no attempt. Hands-Only CPR performed by a bystander has been shown to be as effective as conventional CPR with mouth-to-mouth breaths in the first few minutes of an out-of-hospital sudden cardiac arrest. Conventional CPR may be better than Hands-Only CPR for certain victims, though, such as infants and children, teens or adults who are found in cardiac arrest (whom you did not see collapse) or victims of drowning, drug overdose, or collapse due to breathing problems.

TL;DR Hands-only can be just as effective as normal CPR for the first few minutes after a collapse. It is not as effective in general, and is not the recommended technique it is the "better than nothing" technique.