Pros: Low voltage, great overclocking capability (good binning), value (at the time)
Cons: None really
At the time of purchase you could grab a kit of ECOs for only a few bucks more than a 2x2GB generic DDR3-1333 CL9 kit.
Needless to say, it was a great buy for the price (at the time). These kits are great overclockers, and while rated for 1.35V can run between 1.35-1.65V safely. They can run with lower timings (6-8-6 or 6-7-6 depending on your kit, these come with either Elpida BBSE or high-binned PSC ICs) or much higher speed (as much as DDR3-2133 with higher latencies) stable. They run great when two sets (4x2GB) are installed.
Although RAM prices have changed, the kit hasn't. It may not necessarily be a good buy anymore, but it's certainly still a good kit