Excellent mod, great value for money, great form factor. I love the two battery mode and have used it with various tanks and RDAs for months on a daily basis. Since upgrading the firmware to Arctic Fox I've had a lot of fun fine tuning it and am very happy with it. I experienced a "battery balance" error but found a small wire had come loose inside so I quickly wound it back around the terminal and was back vaping (didn't have my soldering iron handy.) - I didn't detract a star for that because I drop it on average once a day and amazed it is still working.