A buddy of mine has the IPV3 and overall he's pretty happy with it. You should know before you order it that the touch button and charge port aren't actually hooked up to anything on the inside, so they don't work, but that's not a big deal to him. You wouldn't want to use a charge port on this kind of device, anyway - the batteries are hooked up in series (i.e. stacked) in order to get the power needed to drive 150 watts, and charging in series is tricky to do safely. It's much better to take them out and throw them in an 18650 charger together.
The other thing about batteries hooked up that way is that you need a matched set - you'll want to buy batteries for it new and keep them in matched pairs so that you know they're wearing evenly. Use them together, charge them together, and don't use them separately from each other. If you have two batteries that don't match, one can discharge into the other and create battery issues.
That said, the battery life on the thing is awesome. He vapes a lot, tends to stay around 15 watts or so usually, and gets like 3 days of battery life between charges. The power output feels pretty smooth and it's a great vape. We've tried it with his TOBH clone, a kayfun, and a lemo at various power settings, and they've all been pretty great.
Hope that helps.