I've generally been very pleased with the 6.1, but I've come across two related issues with the FM radio app that severely limit its usefulness to me. The first is that it can't be used with Bluetooth headphones, even with a standard headphone cord plugged in as an antenna. On other phones with FM radios, I've always been able to plug in a headphone cord for an antenna while sending the FM radio output to a Bluetooth headset. The FM radio app on the 6.1 doesn't seem to allow this, even with speaker mode turned on.
A secondary issue is that the app will not work if only a headphone cord is plugged in; it seems to require full headphones with speakers. On previous phones with FM radios, I would use a headphone cord with the speakers snipped off as an antenna and send the FM output to my Bluetooth headset. I could deal with this limitation if the Bluetooth issue didn't exist, but it's a bit of an annoyance.
Does anyone know of a way around these limitations? Being able to use the FM radio app in this way makes it great for running, where Bluetooth headphones are much less encumbering than plug-in ones. I had no trouble doing so on the last two phones I've owned, which were otherwise inferior to the 6.1.