Yes, the Dual FFT analyzer is what you want for transfer function measurements.
If you look at the iPhone Tutorials section of our blog, you'll see tutorials for headphone frequency response measurement and loudspeaker impedance measurement. Although they are geared toward specific hardware interfaces, those tutorials can help you get a better understanding of how to configure the Dual FFT tool.
https://blog.faberacoustical.com/wpblog/category/ios/iphone/tutorials-iphone/
Let me know if you have specific questions about your measurement setup with SignalScope.
