I use notcigs VV devices, have an original Infinity and a Buzz Pro. The performance is excellent on both. They have a 15W capability, higher than Provari and, I believe, Darwin, at a lower price point. They adjust over 3.5 - 5.5V. They don't have an LCD, don't measure resistance, all there is to them is a simple thumbwheel to change the voltage and the button to fire them up. $110 is the current price for an I Pro with charger and one set of batteries, about the same as a Lava Tube but a proven, rugged, design. A second pair of batteries and using their coupon code (ECF Buzzkill) brings in a really nice kit at a nice price point.
A true passthrough will indeed be 4.8 - 5V, as it just passes through the USB voltage (wires run through the tube to the connector). Key to them is having a good 2A USB power supply -- I like the $10 IQ Dual USB 2A (Walmart online, $10), which can be used with down to a 2.5 ohm carto.
A regular PC USB is bad to use with a true PT -- it might take out the PC or power supply in the event of a short, and most PCs don't really have enough current capacity on their USB ports. You have voltage sag, over stress components, to drive the PT.
The tank doesn't do too much other than hold a lot of eliquid, keeps the carto nicely wet all the time. I tend to like vaping in the 6 - 9W zone, most of the time around 8W, which leads to the voltages I use. I'll nudge the little thumbwheel a little in one direction or the other throughout the day to vary the warmth and tweak the taste during the day.