A few shades are so dark (blue, red) that the hilighted text becomes unreadable.

The colors are very saturated, which looks nice, but can make the highlighted text a little difficult to read, and I've had some bleed-through on reasonably thick textbook pages.

They almost obscure the text.

(The yellow is a SUPER bright neon.)The other colors are good, although the red, fuchsia, and darker blue are pretty dark - you need to make sure you only use them on very dark text or type or they will partially obscure the words

Can't use several of the colors because they cover up text, like a dark marker

Next comes Sharpie's claim that these highlighters will not smear the text

In my experience with these highlighters, they will not smear pre-printed text (i.e.- a textbook) but handwritten notes (in a notebook or in the margins of the textbook) will smear noticeably

The rest obscure the text and are not useful

Highlighting is supposed to illuminate the text for easy reference but the darker colors make it almost impossible to see.

So if you're going to highlight text in books or other paper, go with another brand that is not as heavy as these, or go with just the yellow; otherwise the text is virtually impossible to read