I have the D4 its got the digital screen. I just bought it from e bay for 24 dollars. Its been working so smooth for me. The price is what got me. And I love yellow and black anything.Had Nitecore I4 for a few years till one of the ports stated half charging, then I got the Xtar VC4.
The VC4 can charge 2X1A or 4X0.5 while the Nitecore can only do 0.5A, it has a better display and even a capacity meter (doubt that it's accurate but still), you can also turn the display off so that it won't blink in the dark.
Cons: the springs are tight which may cause the batteries to fly off when you pull them out if you're not careful (I suppose it will stop over time).
The 2 middle posts are borrow which makes it harder to pull the batteries out.
The usb port is for charging another device like a phone. You need to have a battery plugged into channel 2. Press the button that changes the charge power for one second and plug in your usb device within 30 seconds.I have a LUC for bay charger. I was in a pinch while on business and needed a charger. The shop I went to charger me $55 for a $30 charger. Regardless, it works really well only I can't figure out how to use the USB port.
The latest model of the VC4 XTAR charger is easier to insert and remove batteries while using it. I never had this issue except for when I used an older version of the Nitecore I2 intellicharger.For the amount of use our chargers get, the extra few dollars for an Xtar is worth it to me. I see stories about problems with nitecore's frequently. Don't remember seeing reports of Xtar problems.