How is the quality of alloy sprocket 10 speed sprocket?
There are a lot of small boutique-factories machining extra-weight-weenie parts that serve three purposes:


Provide some weight advantage to very high-end racers who reached the limit of their training levels. That could mean positions in a very high-level race;
Satisfy some folks (whose population is increasing) who don't mind throwing money out the window to have the most exotic and customized extra-high-tech bikes;
Feed the Weight Weenie Contest members with lots of ways to shave weight of bikes they don't necessarily ride (but most probably take a lot of pictures hanging from scales to post online).


(ok, that was somewhat a bitter answer, but I think this is not far from the truth)

And, yes, this means 3 months of riding, then to the thrash can, for the cassette you mentioned. How can anyone afford that?!?!?!?