My take on one right out of the box (that is after i gave it a bath and adjusted the coil to center over the air hole) as you can see i have it on a Twist vaping it next to my DID on a gripper.
After a bath i filled it by turning it up side down and pulling the tank off a bit to fill with my juice bottle, flip it back over and removed the top and gave it a few drops on the coil. After waiting a few short minutes i vaped it and the first few pulls were OK until the 4th pull i got a nasty hit and was like WTF!
so I kicked it aside and vaped on the DID a bit and went back to the Vivi tank and to my surprise it was very good and never a nasty hit, so now after vaping a complete tank full and a tank full on the DID side by side i will say it has promise and is worth buying.
I will fiddle with it after giving it some time in stock form.