This thing works great and I've never seen another product with the same specs. First, it's very nice to have a basic mono Bluetooth amplifier - pretty much everything else is stereo. Great if you have two speakers, but the real problem is when you only want to work with one. Whether you're building a bookshelf speaker as a portable speaker, repurposing an old guitar amp, or renovating something that's massive but not stereo, you're going to run into problems when you try to use a stereo amp - many of these amps aren't unbridged and don't have the ability to mix and match channels, so you pretty much have to force your source device to mono or skip one of your channels (and possibly some mixing). The presence of a built-in mono amplifier easily solves this problem. Second, the battery feature works well. I removed the R01 and replaced the white battery connector with wires going to the 18650 holder and it just works. When plugged into USB it charges and when you unplug it smoothly switches to battery power. It doesn't have an on/off function, so you'll probably want to add a switch to the battery cables if you plan on keeping it unplugged. Finally, the sound quality is quite good, especially at low volume. When you turn it up to about 2/3 volume (on your unit; there are no controls on the amp) it starts to distort noticeably. It seems to work slightly better on USB power than battery, which makes sense given the higher voltage, but you don't get maximum volume anyway. Loud enough or not depends on the sensitivity of your speakers, but a few watts is more than you think.
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