I too love my DSE901 and don't understand the claims of greater throat hit, vapor, etc for the 510. I have both, and they are both automatic batteries with cutoffs, so that is one element right there, I suppose. I also use home made or modded eLiquid with a strong hit, and that may keep me from noticing the difference in 901 and 510 hit. Just some guesses. PGA is the primary throat hit element, and perhaps the hotter 510 vaporizes it finer or something so it doesn't have as much effect... I don't know, I just know I prefer the 901 at this time. Until I get something better.
Here are tips about dealing with cart leakage into your mouth - when you put the 901 style cart in, align the atty so the atty intake hole is at the top, and the flat part of the cart with the intake slit is horizontal and pointed up. Then when you vape, try to keep the hole pointed upward. Because the liquid gets into the bottom part of the cart through the slit in the cart where the flat part is - keep it pointed slightly up, and loose liquid generally never gets down into the cart. You can't do a trick like this with 510 carts because they have slits on both sides.
Next, for both 510s and 901s, blowing into the cart while holding the eCig down will push most of the liquid out of it back into the atomizing chamber, but doing this with the cart on the eCig could potentially push liquid up into the battery (see more below).
If you get a lot of liquid in a 901 cart, take it off and shoot compressed air into the slit on the flat part of the cart and the liquid will all come out the bottom air hole; wipe it off well.
If you are getting a lot of liquid in a 510, pop the back off the cart (if you haven't already for better draw) and daub it out with a paper towel or some polyfill.
Always wipe any excess eLiquid off the side(s) of the cart where the intake slit(s) are when you take it out, also, so you don't draw that into the final cart chamber. When you first put your cart on, have the eCig pointed battery end up and let the wick soak up some of the eLiquid that might be pushed up by the wick. Then point it down a little, and after you point the battery end down, if it's a 510, don't point it up or level again while vaping that cart at least until after the first several draws. Otherwise, if any excess liquid has spilled out, it will run right back into the intake slit(s) of the cart.
If you hear or feel a sort of bubbling in your draw, it means you have excess liquid that is either already in the cart chamber, or is going to run into the chamber if you point it up or draw real hard, so you need to vape lightly with the battery pointed downwards until there is less eLiquid and the bubbling sound goes away. This would also be a good time to either (safest) remove the cart and blow into it while pointing it down, then wiping the excess juice off the cart that comes out, or (potentially harmful to battery) leave the cart on, point it extremely downwards and blow into the hole, a quick short blow. I would imagine blowing into the cart with it on, especially for too long, could potentially get the juice into the battery and short it out, and none of us wants that.
A lot of jabber, but these things work for me. I hope some of it helps someone.