I've heard this complaint often about the eGo-C tanks, and I'll admit that if you don't treat them right they'll probably be a disappointment. That said, I've had nothing but great luck with them, with outstanding flavor and vapor. The only thing I've got that is better is my GG Penelope, but that's a $120 RBA so I'd expect it to outperform most things!
Most important tips I can offer on the eGo-C tanks:
1. When you fill the tanks, don't pop the cap off; use a syringe. (On my four eGo-C tanks, I'm still using the original hard caps!)
2. When you insert the tank into the atomizer housing, hold the housing upside down and insert the tank from the bottom.
3. While inserting the tank, use a slow, firm push with a slow twisting motion. You want the center pin of the atomizer to slip into the tank hole without buggering the edges of the hole. Also, pushing the tank on too fast and too forcibly will create a pressure build-up inside the tank which will result in leaking.
In vaping, as with most other things, if you take care of your tools your tools will take care of you ...