I think these are two separate offers - I had a banner ad at the top of my Kindle webpage yesterday offering six months of KU for 1/2 off, which I meant to post, but just got really crazy/busy and didn't get online to post. This looks to be the same as @Barbara1995's offer.
Then @booklover6's offer with the varying terms and amounts up to 40% off seems to be something completely different. I'm actually happier with the 40% for two years, because I would like to have a membership longer term again, and doubt I would find more 50% offers on a consistent basis in the future. So 40% is good enough for me.
As someone else pointed out, I don't have to read very many KU books to make $6/month worth it.
Thanks to both @Barbara1995 and @booklover6!!!