I have no real experience with the Astra SP blades as I only used a few samples years ago. They shaved okay for me. But nothing too special. I only use the Stainless ones i.e. the Blues. I find them sharp and smooth enough. Actually.... they’re great blades for me! Give those a try if you can. You might like them.
Razorhead
I do like the Astra SS blades. Unlike the Astra SP blades, I find the SS blades to be both sharp and smooth. They are not the sharpest blades available, but I find the SS blades work well for me, whereas the SP blades are barely usable. A lot of people claim the SP blades are both sharp and smooth, but that has not been my experience.