My current bike came with a climbing cassette and i live in a place of flats. So there was no need for that cassette. So i decided to go for smaller gears for more speed. I love it, best upgrade i have done on the bike and it was pretty affordable.
My new bike came with an 11-32 cassette. Living in Illinois, I wanted one that had more intermediate gears since I never need the largest 32 or 28 (for example) with a compact crank up front. So I bought the 12-25 which has a 15, 17 and 19 that are missing missing on the 11-32. The largest gear (25) plus the 34 up front gives me plenty of climbing range for the steeper (but shorter) grades I ride here in northern Illinois and southern Wisconsin. Since I travel to Colorado and Arizona occasionally, I will re-install the 11-32 for those trips.
Going up from a 27 to a 28 was a noticeable improvement since most of my rides are climbing and descending. Going to the 11 speed for the new Shimano groupo was a no brainer. The weight savings of the Dura Ace cassette didn't make sense since clusters wear out before other components other than cables and chains. Overall, really happy with the choice.
With 11-speed components still being fairly new I am always aware that there may be bugs. This cassette has far exceeded my expectations (though I probably should have know that coming from Shimano it would be great). well made, fits perfectly and moves smoothly. The teeth grip the chain and alow for easy shifting from 1 gar to another. Happy to have 11 usable cogs for each ring )