I have a pair and they work fantastic in stereo. Once you pair them the first time they'll automatically connect to each other when you turn them on, and the buttons on one will control the other. So if you change the lights or turn on Bass up on one, it will do so on the second unit as well. Even the power button syncs, you you can quickly turn them both off.
My only issue is it is hard to tell which one is which channel, though I don't know how they would solve that (maybe have a firmware update make a button combo flash the leds?).
Stereo mode supports Aux input, Anker support told me otherwise but it turns out it works. Also the auto-shutdown does not occur if they are plugged into a charger, so if you wanted to you could set these up as computer speakers or something. Maybe hook them up to a Chromecast Audio.
My second unit originally had the fabric a bit messed up, but Anker quickly replaced it for me.