Humminbird's Quadrabeam transducer (P# XNT9QB90 and T) work with the following units:
1157c
1158c
300 TX
400 TX
717
718
727
728
737
747c
757c
767
768
777c2
778C
778c HD
787c2
787c2I
788C
788ci
788ci HD
917C
931C
931C DF
937C
937C DF
957
958c
MATRIX 35
MATRIX 37
PiranhaMax 180 (tri beam only)
WIDE OPTIC
WIDE PANORAMA
WIDE PARAMOUNT
WIDE PORTRAIT
WIDE VIEW
WIDE VISION
Basically it adds the additional 35deg sonar cones on top of each side of the 83Khz (60deg) cone to open up the field of view to 90deg of coverage, offering a true 2:1 ratio of the bottom. Eg, if you're in 4' of water, you'll have 8' on the screen. In 8', you'd have 16', etc etc.
It does open your field of view, but it's not side scan by any means. I read a lot of concern about the narrowness of the cone angle at the extreme edge of the beam, as you'll loose a lot of the water column above the angle.