I've owned both a Sigelei 150 and an IPV4.
As others in this thread have said, the Sigelei is a brick. Mine took a tumble onto asphalt from 6 feet, and survived.
The only issue I have with the Sig, is how it feels in the hand. It has been a solid mod otherwise.
It was recently passed forward to a friend who was ready to step into the sub ohm
tank world.
The IPV4 has held up very well (black), no scratches in the paint. I just recently received the silicone case for mine, and I like it even more now.
My main concern with the IPV4:
-The charging board. Which really should be removed, due to the issues folks are experiencing. There have been reports of the charging board shifting, and causing a hard short on the 510. This has happened to people who are NOT using the on board charging. I've removed mine without an issue. (Two hex screws, clip three wires, cap the wires, replace the screws).
-The battery sled holds
batteries in place a little TOO well. While it has a strip to remove the batteries easily, using it results in the wrap on the battery tearing/bending on the pos/neg terminals.
I would suggest holding both the sig150 and ipv4 in your hand before making a decision. Personally, the ergonomics of the IPV4 are worth having to remove the charging board, and re-wrapping two sets of batteries every week.