I have never tested a face primer with "blur effect" which I have thought is bad, but now I have even got a favorite! :)
By blur effect is simply meant that it fills the pores and makes the skin look (and become) temporarily smoother. You can use it both with or without makeup on top. I do not have a huge problem with visible pores, but they are visible enough for me to be able to show you how big the difference will be on me!
My new favorite that I think is really good is NYX Pore Filler! It costs SEK 195. Here is my result:

Surely it looks like the afterimage is just blurry and blurred? It's not! I have cropped the image so that you can see up close, but at the bottom of the post you see the full images and that both are sharp :)
What I like about NYX Pore Filler which I think is a bit better than other brands, is that the difference is greater even when you are unmade up as it "blurs" irregularities in the skin tone nicely too!
The result is silky smooth, you get a smoother surface (which is also worth gold when you then apply foundation) and the skin becomes matte and fine. Can really be recommended!
Available for purchase at HERE.
Two thumbs up!