well i can see where hes coming from, but on the other hand, a derailleur is a simple mechanical system, consisting of a cable, a spring, and a hinge system. The most important parts are the tension and quality of the spring, the durability of the casing, and the strength of the mounting bracket. Ive used both shimano acera and shimano altus. The altus was crap, as i had two. The spring was so weak that the adjustments were imposiblle to make it shift well enough to not cause stuttering and waiting for it to shift. The acera is a good shifter, but still has a few weak points, suck as the flex when hitting big bumps and shifting at the same time. I have never used SRAM before, so thats why i asked if the X-4s were good for a 300 dollar bike with basic components on it.