They are the same unit except you left off some of the model designations.
There is only one G2N SI model and that is the MEGA SI.
MEGA means 1.2 MKz (1200 kHz) Imaging.
There is the discontinued Helix 10 SI GPS and it has no CHIRP sonar or CHIRP Imaging like the MEGA units have. That model is on close-out sale by several retailers.
Do a web search for CHIRP Sonar.
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