Bought the same in 8mm from Whitworths five years ago. Didn't last much longer.
Went to 10 mm in the other "quality" chain they keep. Idea was at least there is a bit more steel? Gal has lasted a bit better. Still not nearly as long as you might hope for the price.
Not sure how true it is, but have been told even the good chain is sent to China to be galvanised?
Whether you anchor on sand or mud and how often the boat swings can make a big difference? Still, that 8mm PWB I bought was ****!