The only model I had ever used was the 510 that I started with but very quickly got tired of switching batteries. I then got on the modders forum and found out how to build a nicostick(box mod) and really like it alot. The 510 with the bigger battery behind it makes it a totally different pv to me. I was curious though about the other models so I ordered a couple 801 attys and some cartridges to use on an 801 box mod that I built yesterday. The 801 seems to hit a little harder and produce more vapor than the 510 using the same parts including a 14500 battery. I am liking the 801 quite a bit. The larger cartridge is quite a bonus. It almost seems like the 801 uses more liquid or maybe it uses it faster. It could just be my imagination. Anyway, just a positive experience that I thought I would share. I am curious though if others who have mods prefer the 801,901,or 510 with the larger battery.