Working With Developmental Editor

Dear Rich: I am developing a book and I'm considering working with an editor who will assist with development. The editor sent me a confidentiality agreement to sign basically protecting her company in the first part and protecting me and my book idea at the end with these two paragraphs. 

The Author’s commitment to maintaining the confidentiality of Company’s Confidential Information shall not extend to information the Author already possessed at the time of disclosure by Company, information which is in or subsequently becomes public domain, whether through release by Company or through a source other than the Author. 

Company understands that the Author will share information about the Author’s work, including, but not limited to, draft manuscripts and/or concepts for a book or books (hereafter “Author’s Confidential Information”) with Company during Author’s dealings with Company. Company agrees to keep Author’s Confidential information confidential, except as necessary to provide services to the Author.

I wanted to know if that’s all I need for an initial meeting with a book development editor. 

We're excited because this is the first time that a reader and the Dear Rich Staff went to the same summer camp -- Camp Lohikan. We have fond memories of our times there but we're glad we got out before the Honda dirt bikes arrived.
Right, you had a question. The first paragraph, above, is a typical "exclusionary" clause from an NDA and we explain its purpose at our NDA site. It's nice to have this clause but its absence probably wouldn't make much difference, as a court would insist on these exclusions even if they weren't part of the contract. The second paragraph establishes that confidential information about your book won't be disclosed unless it's required for the Company to do its job. You might inquire as to what types of services require disclosure. If concerned, you might even insist that the agreement be modified so that your permission is sought whenever the Company discloses the book to a third party. 
Is that all you need for the meeting? You could have an attorney look at the remainder of the contract, or you could review the basics of confidentiality agreements at our site. And of course, if you have sufficient clout in negotiations with the editor, you might want to consider providing your own contract. That agreement could sort out any copyright or ownership issues or prohibit the editor from publishing a work that competes directly with your project.
Who do you trust. Mostly it comes down to trust. The biggest issue for you is whether the editor is reputable and whether you can trust her. Generally, it's difficult for an editor with an unethical reputation of stealing book ideas to stay in business for a long time. So if an editor's been around for many years, that may be an indicator of trustworthiness. Perhaps you can also ask to speak with other clients, as well as checking the editor's reputation online.