Question in response to your replies
Thanks, Bob and John, for your helpful replies.
May I assume it would be safe to download a couple more extensions if they are from the official Google Chrome Extensions Gallery and have, for example, 30,000 or more users? Seems either Google or a programmer who can detect malicious code would have caught any untrustworthy extensions within those parameters, but I want to be on the safe side.
Here is one I want and looks perfectly safe to me. The main reason I post the link is that it has an interesting explanation about the warning message and the developer's need for this specific plugin to access data, and how far it will go. I haven't seen an explanation like it before.