Everyone has seen many jokes and videos made about the lack of phone jack on iPhone 7. You could put a 3.5 mm to a lightning adapter, but that would mean you cannot charge the phone at the same time.
The RES converter was designed as a solution for dual charging and listening. Instead of purchasing completely new add-ons, The RES external digital-to-analog converter (Hi-Res DAC 24 bits 192kHz) attaches to 3.5mm jack and lightning ports, allowing you to play audio and stay charged around the clock… More at kickstarter.
Potentially a very good product and especially if the sound is markedly improved. Would like to see a more original design though. It looks a bit clunky to me.