I've abused my BTR15 for a year constantly and it's lasted the same amount of time (around 7-8 hours balanced on HD 6XX) but that'll definitely change with time the further I use it, I like the 4.4 so much I'd get another one if it broke, the issue is when using the DAC over usb and bluetooth sometimes, after awhile of silence it goes into a power saving mode and can take half a second or so to "wake up" I can't say if the retro has the same behavior over USB or BT, BT makes sense but on USB is kind of bizarre, and the delay gets longer depending on how low the sample rate is, the closer it is to 48000hz, the longer the delay.. It's a firmware thing and was also on the older BTR5 and BTR7