The most common and most likely answer to this crossword clue is the 14 letter word INDECIPHERABLE
I've seen this crossword clue in The Sunday Telegraph
I
N
D
E
C
I
P
H
E
R
A
B
L
E
More clues leading to the result INDECIPHERABLE
Buddy explains!
The straight part
We know that "not good for readers" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case not good for readers = indecipherable.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does INDECIPHERABLE mean?
INDECIPHERABLE adjective- Not decipherable; impossible to decode, read, understand or comprehend.