You will find a highly technical scientific comparison between jpeg and filtered jpeg in this International Journal of Computer Operations article. If you are not interested in the mathematics and comparison tables in the article, the conclusion is:
Originally Posted by International Journal of Computer Operations
However, all the decoded images resulting from this approach and original images are almost the same in human perception point of view.
In other words you are not the only one that can tell little, if any, difference in jpegs and filtered jpegs other than a reduction in the file size. There are other factors that can and will have a highly noticeable effect on jpeg image quality.

If image quality were important, JPEG would be at or near the bottom of my list of choices.

If we knew what it was we were doing, it wouldn't be called research, would it?

— Albert Einstein