Like Ven, I too have both the VC4 and the Opus BT-3400 (US version, same charger) and I think that for $20 more, you'd be better served with the 3100/3400 than with the VC4, unless for some reason, you need it for its USB 5v input--say to run with a USB solar panel.
It does more, does most of it pretty well and I got mine with a 3A cigarette/car adapter, so I'm good there. The VC4 is a good deal cheaper, but I've left mine at my GF's place and use my Opus here, or my Xtar VP2.
She better figure it out quickly, since Hurricane Matthew is blowing through town over the next 10 hours.
I wish her well.
Chris