I wasn't certain whether to invest in a variable voltage device, so I decided to give the 4.8 volt NiMh batteries a try on my 18650 battery APV. The 18650 and 4.8 NiMh are the same size. I rotate three of them. I have definitely noticed more vapor and throat hit, and improved flavor notes with certain juices. As expected, they don't last nearly as long as the 18650 AW IC 3100 mAh batteries I was using, but the quality of the vape is much more satisfying.
For those folks that are contemplating giving 5 volt vaping a trial, I can recommend these batteries. They are not protected, but they allegedly are a "safer chemistry" battery. They do need their own special charger (make certain you get the newer charger that lets you know when batteries are fully charged), but the recharging times are very reasonabe and I can get thru the day on 3 batteries with moderate vaping.
Somewhere in my future I will get a variable voltage device. Like others have said, once you experience higher voltage its a little tough to go back.