I've had one 510 PT which worked very well. IMO, the ones which don't have an inline battery will give you the best performance.
I think the inline battery moderates the power delivered to your atomizer. Notice I said I HAD one ... most of them are fairly fragile and don't take much abuse. I've been pleased with them though.
Some people caution against plugging directly into your computer due to a tiny chance that a faulty PT could fry it. I believe there is one documented case of this happening. But, you can also use them via a USB wall wart power supply, or a battery pack.
PTs are great for road trips. You'll need a power port USB adapter with at a minimum 1000 mAh, and more if you can get one up to 2000 mAh. TMI?