I agree.  Knowing it's limitations is the key. It isn't difficult to know the limitations. They are clearly stated in the disclaimers and service agreements of the online sites. Typically the disclaimers state the limitations this way, "use at your own risk, not official, accurate or complete" In other words, unreliable for any purpose except the most casual.

As abstractors we ask our clients to rely on our reports to be accurate and complete as derived from the official public records. Our clients in turn rely on us to use accurate, complete and official sources.