I just got my 510 equipped Chuck Tuesday night and I wanted to compare with my 510. Here's what I did. I let the 510 battery charge for 6 hours, and used a brand new, never-before-used 18650/3000 battery in my Chuck. I tested both side by side, each with brand new atomizers from TW. I used NHaler 12mg High Voltage Pina Colada juice in both.
What I found was that for the first hour or so, vapor production was nearly identical. After that, my 510 started a slow drop off. Another 2 hours later, the 510's LED was giving it's tell-tale rapid blink of battery death. The last real hit I got off of it (that is, a regular draw that didn't end in a blinking LED) produced appx 1/2 the vapor and throat hit as it did at full strength. The Chuck experienced no change.
This test was very much less than scientific, but as far as I'm concerned, it proved the advantage of consistency with the Chuck (and I would imagine any decent battery mod, as the Chuck is the only one I own at this time). The only other difference I noted was the Chuck's vapor was slightly warmer. I think this may have been a difference noticed over time. Perhaps both the 510 and Chuck produced appx the same temp of vapor at the beginning, but as the 510 battery dropped off, the warmth of the Chuck's vapor became more apparent. The warmth enhanced the flavor, I imagine much in the same way those warming air fresheners deepen the smell of the oil packets you stick in them.
The bottom line in this is that the advantage of a battery mod is having the effects of a freshly charged battery for a longer period of time. Mileage, of course, will vary.