I tried this with the stock filler, and it filled easily without a syringe or any other manipulation.
But it did leak a bit when it was full, which I consider a good thing.
It was a good indicator that it was full.
So it gets a 8/10 for ease of filling.
I had to mess with it a lot while drawing on it though.
I got some juice in the mouth once, which NEVER happened with my 510 before.
I also got leaking and flooding when I stood it cartridge side up.
I got it worked out after awhile though.
I found that I can cover the hole with my lips while drawing, or not.
Letting the hole go uncovered means more juice flowing.
Covering the hole means less juice flowing.
I would start the draw with my lips over the hole to smoke what was already there.
And then I would draw my lips back off the hole to finish the drag.
That would help bring juice up for the next drag.
But in the end I found it to be a pain.
So for actual smoking utility, I have to give it a 5/10 rating.
The blue foam was working better for me, without as many hassles.
If I was doing something wrong, tips would be appreciated.