Having both the sigelei and the IPV3, in my opinion the IPV3 is much superior to the Sigelei. I wouldn't buy one from overseas, as I did that with the IPV2 preorder and then discovered that the overseas warranty was much more difficult than the US warranty. So this time I bought from Vapor-Tek USA and everything has been great so far.
The Sigelei 100 has worked pretty well, I've been using it since the first shipments began, about 3 weeks I believe. The IPV3 is of much better build quality, I like the button better on the IPV3. I expected to like the button on the Sigelei more as it looks like the buttons we use on custom box mods which is really solid. That's only appearance, as it's more of a very soft, short digital clicky throw than a shorter but similar to horn switch type throw and feel.
For instance, the sigelei if set on it's side with fire under it's own weight. The IPV3 feels much better in the hand which is a nice lil bonus, and it looks so much better, I switched over to it for a more formal business function because it's so sexy and classy with it's machined beveled edges.
Overall, for right now I will say that if this experience continues I'll be selling the Sigelei to put towards my hexohm v2 or another IPV3, because I just don't see a reason to keep it with me liking the IPV3 so much better.
I didn't consider the added power of the IPV3 or upgradeable firmware in the IPV3 for this brief comparison review. I think both would be big pros, but the average vaper doesn't need more power than stock and I wanted to review it out of the box, because most people don't need to update the firmware.
For the record, as an IPV2 owner with problems I wasn't planning to lean in this direction, but the build quality improvement is drastic, and P4U addressed more user feedback I've ever seen in such a short period of time and most of the complaints from IPV2 users after launch were fixed and addressed with the IPV3, it really looks like someone at the manufacturer took the IPV2, used it, shook it, pressed it, vaped it, and said "what would make it better" and then read the forum threads. That's a big deal, and the improvements and fixes helped in my finding so many pros with it.
The sigelei magnets are nice, but I had one pull out, I'm not sure when it happened because it stuck to the battery cover and wasn't immediately noticable, but I didn't lose mine or it would be a bigger problem. I see this being an issue in a few weeks when many more start showing up.
