I have both & like was said the DE89 is a mild razor but, its hard to get irritation from it on the neck area. I know where my trouble spots are & go over them a couple more times getting a close shave. The Astra SP blades can contain duds I have found out.
You saved me so much trouble! Thank you!
I used Astra SP with many different razors and it was one of the worst blade. I thought there was something wrong with me. After all, the big majority writes that it is among the best blades. (So, I am the wrong guy).
I used it after two months. The same disappointment.
Today I read that Astra SP blades "can contain duds".