Humminbird Helix MSI Question

I have a Helix 7 MSI G3 and a Helix 9 MSI G3N and I was wondering if someone can help answering some questions

1. The transducer on the Helix 7 MSI G3 is only 3.5" long but the Helix 9 MSI G3N is 8" long. They are both Mega units so what is the difference?
2. Can I have both transducers on the back on the boat and use on for full screen side imaging and the other for down imaging and running both the the Mega hertz Frequency. Will it cause interference between the units?

Thanks

The SI transducers for the Helix 5 and Helix 7 are Compact SI==less expensive than the larger MEGA SI+ for the larger units. You purchased the low end of the product line and that is what you got.
Also the SI models of Helix 5 and 7 don't have Down Imaging, they have simulated (composite DI) views created by blending the two SI pulses==no Down Imaging piezo in the transducer.
The larger MEGA SI+ transducers have a Down Imaging piezo and the circuit to support it.

Sonar units WILL cross-talk when their sonar pulses overlap on the same frequency and screw up both units. It's a sure thing with both on the transom.

Appreciate the answer again Wayne. Not only you know the functionalities to these unit but are wiling to share your expertise with us. Awesome !!!!