If you can stretch your budget I would go with the G2 Helix 9
http://bbgmarine.com/humminbird-helix-9-chirp-mega-si-gps-g2n-combo-p-23614.html This unit gives you the mega frequencies, chirp 2D, DI, and SI with a dedicated DI element.
The Helix 9 in your link is the previous generation unit and comes standard with the compact SI transducer. That can be swapped to the HDSI transducer for $65 but now you are getting closer to the G2 unit. The Helix 7 G2 series SI units also do not have the mega all in one transducer.
I think you will be a lot happier with your purchase if you save a little longer and go with the 9 mega unit.