Disclaimer: Fiio supplied the BTR1 for the purposes of review at Headfonia.com. That review will reference this page. The BTR1 goes for about 50$ USD. You can find out all about it here: Fiio BTR1.
I get over 7 hours on a single charge, and notice very little hiss at all. It shows a certain amount of frequency oscillation, and moderate levels of jitter. Next to Astell&Kern's more expensive XB10, both are minimal. The BTR1 sounds, and measures, good.
What bothers me about it is that both its reception quality and signal stability are just so-so. I've had it stammer at two paces, though unobstructed line of sight can get up to eight. But turn your back, or pass a well-muscled arm between BTR1 and its wireless source, and st-st-st-stammer it does.
No matter how well the BTR1 holds load, no matter how good it sounds, its one job is to pass wireless signal to earphones. If it can't do that reliably, it fails at everything down the line.
While nearly nailing the audio groundwork Fiio screwed connectivity. Ho hum.
NL - no load
SM2 - Earsonics SM2
ES7 - Audio Technica ES7
DT880 - Beyerdynamic DT880/600
24-bit single ended @+0dB - all targets
24-bit single ended @+0dB - summary
This thing needs a plastic version, with a damn good antenna, or it won't make a dent in anything but the wall.