The Buzz @ notcigs.com is a nice unit for variable voltage. That simply made vaping GREAT for me. Don't have to worry about low res this and low res that... you just adjust the voltage on the unit. For me, 3.7 wasn't enough, and 5v was a bit much. With variable voltage you can dial it in to exactly what you want... 4.3 - 4.5 for me.