I personally think quite highly of JG guns for the price. However, I also realize that there's a lot more of a chance of failiure with one than with a high end gun like Classic Army or G&P. However, considering the JG is $350 and the CA / G&P equivalent will cost upwars of $650, it's a matter of getting what you pay for, really.
That being said, I've put my JG guns through hell that would have probably killed most other guns, and they've performed flawlessly. Whether I got lucky or that's a common trait with JG, I don't know.