I have used this Shimano cassette before too .
I used to have a microshift 11-40 cassette which was 585g. The Shimano 11-42 weigh only 480g without the lock ring. Im not sure if it fell down during transport or they sell the cassette without it. Not a big fan of Shimano packaging, they should just put things inside closed boxes rather than half open ones.
Super smooth wide range cassette ... 11-42T. Shifting performance very good. I am using it on my firefox tornado.
This cassette is very helpful for hill riding