I love my egos, I have two, one 650mah and one 1000mah... Works great with my 6ml dct, and low res. Cartos are just bomb... Kgo.. ego... They are pretty close in comparison from what I can tell...
They look the same, but with the ego, you'll be vaping at 3.4V. With the kGo, a good part of your vaping, while the battery is freshly charged and for several hours afterwards, you'll be vaping at the high 3's up to 4V. That's a big difference in how many watts you can deliver to the coil.
they batteries are basically fixed so if they burn out you basically have to use a different vaporizer unless you buy the batteries and disassemble the vaporizer yourself, which is a little tricky, but not automatic. The only problem with the 2% defect rate is that if you happen to have more than a 2% defect rate than you have to pay for shipping of the replacements even though they pay for return shipping of the defective ones.