But is it worth $100 to have some decent microphones connected to a machine with a complicated set-up (and app install) involved

The microphones work well - better than some cheap standalone microphones we've bought to sing with connected to a stereo system while playing youtube karaoke videos

My daughter received this machine as well as the Singing Machine SML605W Agua Dancing Water Fountain Karaoke System with LED Disco Lights & Microphone, White from Amazon for review.

The microphones work well - better than some cheap standalone microphones we've bought to sing with connected to a stereo system while playing youtube karaoke videos