On the shimano.com website, the HG61 is not SLX and it is DEORE. The HG80 is SLX. There is a big difference in the weight and price. I made that mistake already.
It is a good buy if you don't mind the cassette weighing 400grams as opposed to 300grams.
It is a good buy if you don't mind the cassette weighing 400grams as opposed to 300grams.