With the regular 510 manual you can use 510 cartridges and atomizers or cartomizers or tank atomizers and tanks. I have all of those and they all work together just great, though the tank setup is my favorite.
I do believe everything would work fine with the mega battery as well.
It's also way easier to find extra batteries when just dealing with the 510 instead of the 510-t.
The chargers are different, everything I've read says you can't use a 510 charger with a 510-t battery and vice versa. No clue why they even have a separate type with some of the 510-t setups if everything works with the regular 510.