You don’t have to delete the ON app. You can just leave it installed in case you want to use some other functionality on it beside the program change and volume control. There’s no conflict to have it installed. I have it installed myself. But I rarely ever open up the ON app to use it for program change or volume change. I either use the actual buttons on the OPN for that, or sometimes I use the MFI menu for that.
But the Bluetooth connection between the OPN and the iPhone is actually done via the MFI functionality on the iPhone, that is, you must have gone to the iPhone MFI settings to pair up the OPN to the iPhone initially.
The ON app, when you open it up, will try to connect to your OPNs initially before you can use the ON app. But that’s not the real connection between the OPN and the iPhone. The real connection between the OPN and the iPhone is via the MFI pairing. The ON app simply connects to the OPN THROUGH the iphone. If you hadn’t paired the OPN to your iPhone via MFI, the ON app will not be able to connect to your OPN. In fact, if you hadn’t paired the OPN to the iPhone via MFI and you try to open up the ON app, it’ll tell you that you must pair the OPN to the iPhone via MFI first before the ON app can connect to the OPN.
By the way, you can hear hands free from the iPhone, but you may not be able to talk hands free with the iPhone if your iPhone is too far away from your mouth. You’ll either have to hold it near your mouth or set it on a table right next to you or put it in your shirt pocket up side down such that the mic is near your mouth enough to pick up your voice clearly.