There is no G2 Helix 9 or 10, just first generation and G2N models.
The 10 has a higher resolution display (about 3,000 more pixels per square inch) plus having a larger display.
The physical size is the same.
"Worth" would be your determination. In all cases BIGGER is better.
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