Should we use confidentiality agreements to ensure confidentiality from our developers?

Yes. You should use confidentiality agreements. For several years I was the editor of West Thompson's leading treatise on this subject, "Employee Noncompetition Law." In this book I review the pros, cons, advantages and practical tips for using confidentiality and noncompetition agreements with a variety of associates (be they employees, independent contractors, joint ventures, etc.). A confidentiality agreement will best help everyone to understand their duties and responsibilities. I recently posted a short article that touches on some of these issues at https://www.linkedin.com/pulse/how-protect-your-business-clarity-communication-steve-lundwall?trk=hp-feed-article-title-publish.