Hummingbird 597ciHd/w Gps -OR- Hummingbird 597ciHD w/GPS and Down imaging? $ difference is about $150. To be used on the bow on the Trolling Motor. Which one do you suggest and or prefer and why. I already purchased the one without the DI but haven't opened it yet and may exchange it for one with DI if you guys think it's worth it. Thanks