I have a mod with digital variable voltage adjustment capabilities, and have vaped with both the 510 and the 901. It is clear that the 510 gives off MUCH more vapor at lower voltages and way more flavor. I can vape the 510 at 3.3 and be completely content with the amount of taste and vapor. Though when using the 901, if I vape at 3.3 volts I need to take a 10 second manual vape to come close to the vapor amounts on the 510 (SLB 2.0v Reg 510 atty). If I crank up the voltage to about a 4.0 on the 901, its starts making a really good amount of vapor, but my main concern is the very short amount of vapes it takes for the 901 to get hot at that voltage. After 5 vapes at 4.0, it is considerably hot (not too hot to touch, but enough for you to think maybe you should change it out temporarily). I do like to have this in my collection though as it gives off a very smooth, cool vape. It saved the day last week when I had ordered some mocha flavored juice, and the place which I had purchased it unfortunately made a VERY harsh mix of flavor. Using the 510 with this juice was just unbearable, but with the 901, it was thankfully VERY tasty, and smooth. So my conclusion is that the 901 is definitely not a monster by any means, but can be a very useful tool for a veteran vaper, or even someone who just happened to get some harsh juice lol.