It works if you follow the instructions. – HK Connect Review

I own two HK Onyx Studio 4 speakers and can consistently utilize the stereo/party function this app offers. You can merge two speakers without this app. However, it is required if you wish to listen to the music in stereo. No issues. Just follow the step-by-step instructions in the app or the included handbook.
Review by Ocrizo on HK Connect.