Bicycle parts are expensive. Spend more money and you typically get stronger, lighter, and better-performing parts. But spend enough money, and "better" may begin to mean "weaker". Here's a graph to illustrate how that can play out. Notice how strength drops as cost skyrockets.
A friend today asked my help for his mountain-bike derailleur. It's a top-of-the-line SRAM X.0 nine-speed derailleur with a list-price on Amazon.com of $253.00. Ironically, that $253.00 buys a purposely-weaker part than the one-step-down X.9 model listing at just $97.00.
Two and half times the cost for a weaker part? What gives?
The answer lies in racing. Bicycle racers have the singular goal of winning, and the rider with least weight on the bike gains an advantage. My friend's X.0 derailleur is made with an aluminum B-limit screw in pursuit of weight savings, whereas the X.9 derailleur comes with a steel screw in that position. The aluminum screw snapped during some aggressive riding.
We replaced the failed aluminum screw with a steel screw taken from my X.9 derailleur. The weight gain is negligible. Steel is robust and won't snap. My friend can ride in confidence that his new B-screw will hold up to his aggression.
More expensive is not always better. The X.0 derailleur is for the well-funded racer willing to risk broken parts in eking out the last bit of advantage in a race. The X.9 model is more of an "everyman" solution for aggressive riders who won't win or lose over a single ounce. Which is better? It depends upon the type of rider you are.
Think carefully when shopping beyond the sweet spot in the value curve. Research the tradeoffs being made. Then make the right choice -- for you! -- on whether it's worth it to more than double your cost to save an ounce.
I'm the original owner of that bike having the X.0 derailleur. A bling bike to be sure, and my friend rides it the way it was meant to be ridden. I learned from it and others that after a certain point I'd rather have two more modest bikes than a single very expensive one. Today I would buy the X.9 derailleur. I'm the everyman, not the racer.