My two cents; The 4 cell Trustfire box I own ( with USB connector ) should work fine if I should chose to keep a GPS or cell phone charged. The thing is I don't use the cell holder for powering my bar lamp. I use mine to power my helmet lamp. Yeah, I could charge my phone if I had to but then I'd have to put it in my hydration backpack along with the cell holder.
On my road bike I'm more prone to want to use an external USB outlet simple because I use my phone for navigation and for playing music ( mounted to my stem ). My phone is new so for the most part I really don't need to charge it during my usual 1-2 hour rides. If I did take a longer ride I would most likely buy one of the MS linear USB converters and then buy a "Y" extension so I could run both the USB and bar lamp from my normal 2 cell battery pack at the same time...OR...I'd just use the Trustfire 4 cell holder.
Keep in mind that the TFire cell holders and the MS USB DC to DC converter both output around 2A on the USB side. That's fine for most phones and other small USB stuff but if you have a USB lamp that draws more power you might be better served with a dedicated 3A output USB battery bank.
Almost forgot, I did buy a 3A USB output DC to DC converter ( off of Amazon ) which should work with any of my bike batteries. I've just been too lazy to wire it up and truthfully I almost forgot I had it. Maybe in a couple weeks when I'm off I'll mess with it.
