I think Geoffs attys work great at 5v. I have been vaping his Tobacco juice and the combination of his atties with 5v is a total sweet spot for that juice. Mild like a 901 but nonetheless flavorful at 3.7v. I would compare them at 5v to an authentic Joye 510 at 3.7. This may be because his atomizers are 3.2 ohms. I had several 'go south' on me, and the only problem I seem to have with them is I have to loosen them up a bit on my 5v box-mod to get good air-flow - a good draw -. Great performers though. And if i compare them to any other name brand, nothing has lasted for me.