As an accomplished professional in mobile app development, particularly experienced with Android devices, I bring to the table a variety of skills that directly align with your project's requirements. Among my many accolades, I've built fully functional and optimized apps on both iOS and Android platforms for more than 18 years. Integration of IoT devices is another area where I have proven expertise, which will undeniably contribute to the smart scale functionality you're seeking.
Moreover, given your emphasis on user-centered design and overall appeal, my know-how in modern UI/UX principles will ensure maximum satisfaction for your end-users. However, what sets me apart not just delivering applications but going miles ahead in providing comprehensive documentation, effective communication, and flexible revisions through my excellent track record and rave client reviews.
In conclusion, a project as comprehensive as yours requires a seasoned developer who understands the intricate nuances of IoT integration along with cross-platform compatibility while maintaining data privacy. With my extensive skill set and unwavering commitment to quality, I assure you the delivery of a cutting-edge fitness app within the stipulated time-frame - one that's engaging, secure, fully-functional across all platforms and encourages users to lead healthier lifestyles.