I have several PTs from different suppliers, one of them being from V4L, and I can tell you that the V4L one is great. I use it in my car (with the USB lighter adapter that they sell on their website) all the time.
I could be wrong but I think you lose a little power when using it in your car, as opposed to a USB connection at home, due to the adapter. I could be wrong though. Either way, I still feel like it does a great job in the car.