The most common and most likely answer to this crossword clue is the 13 letter word LABOUR-SAVING
I've seen this crossword clue in Independent
L
A
B
O
U
R
-
S
A
V
I
N
G
Buddy explains!
The straight part
We know that "It’s so efficient" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case it’s so efficient = labour-saving.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.