Since I'm learning how to sing and using a mobile app for that and regular headphone microphones are not meant to be used to record vocals, I bought it and I'm using it to connect my XLR microphone to my mobile device. I'm very happy with the outcome and I can't complain.
The on/off button is very useful and so is the gain knob.
As for the battery, I bought a couple of rechargeable 9v batteries and I don't have to worry about buying batteries anymore. By the way, the device doesn't consume a lot of power. I use it almost every day for a couple of hours and change and charge the battery almost every week.
The price was affordable and I highly recommend it for vocals recording.