The MEGA SI units have 455 kHz, 800 kHz, and 1200 kHz Imaging and their CHIRP ranges also.
As I stated in the BBC link, I use 455 kHz for fishing due to the wider coverage.
I don't fish for crappie, but I see them a lot. Comparison of 455 kHz with an ONIX and 1200 kHz CHIRP with a SOLIX of the same school:
Edited by Wayne P. (08/09/17 05:31 PM)
Humminbird Helix 12 CHIRP SI, 1198c SI, 1198c SI, ONIX 10 SI NT, Helix 7 CHIRP SI GPS G2, SOLIX 12 SI, 360, RC-1