The u coils are stellar. My wife and I used these as our main device when we started. With light colored, non sweetened juice we could go 3 weeks on a coil. It is a great little piece, but using it as our main device soon brought out its' shortcomings. We kept them for our backup unit.
Don't try to monitor the charge. It will drive you crazy. When it is fully charged the light is supposed to be red and orange, but it is actually pink. It will stay on pink for about 10 puffs, then it goes to blue. It stays on blue for most of the charge. Then all of a sudden it is orange, and 5 puffs later it's dead. Also you can't see the charge light unless you are in the dark. I bought the charging dock to help. You can take the dock with you and charge it when you are out. However, there is no charge level indicator on the dock. When it turns red it is dead. You just have to remember you get about 3 charges out of the dock.
It's almost impossible to see the liquid level if you use light colored ones. It doesn't hold much, so you have to take liquid with you if you are gone for a full day.
Filling it if you are out is messy. As you know, you have to unscrew and take out the whole coil/air shaft to fill it. Don't ever fill over the red line, you'll regret it. It's hard to line up the red lines when filling it.
If you vape frequently, you will only get 4 hours out of a charge. It's just too labor intensive to be an all day vape unit. Also, the airflow is too big for true mtl. Pulls too much air. Don't get me wrong, it is a great little deal, but everyone I know uses them for a backup or for stealth vaping at a 3 or 4 hour event.
Do yourself a favor. Look at the Innokin Endura T18 or T22. Hands down the best mtl device available. Watch Phil Busardos hour long review. And keep the Breeze as a backup. I think as time goes by, you might tire of the attention you have to give it to go a full day and night of vaping.