I wouldn't trust an outside vendor. Getting into things like unlocking is entirely different territory from the mainstream retail world. You don't know exactly what they're doing to it, and if it breaks down you can't go back to the manufacturer for help in this case.
Yes, fully reversible does mean you will be safe for future updates, or even situations where may need to have Apple service the device. You just have to revert the software back to factory specs, which is possible and easy with Pwnage. Plus you can revert back befor updates so your phone isn't bricked. However, chances are with the Pwnage method you won't need to. I can't go into details, but computability with future updates is already almost assured, and even if it isn't you can either put off updating until it is or go back to factory until it is. This is the essential capability that makes this particular method superior, and makes using other methods or buying a phone unlocked a bad idea.
You probably have reservations about doing it. I won't lie and say it's full proof, but no unlocking is and it's better for you to know how it's done and what you're doing in case something does go wrong. And to be honest, it's not that hard at all. The developers have made it a very simple point and click GUI interface. With a little reading, you shouldn't have a problem doing it yourself.
