MTB, the finder you're looking at appears to be down imaging (aka: down vision) only. I like DV as an added feature to a traditional sonar but alone it might be too limiting. On my aluminum boat I have a Raymarine Dragonfly Pro 4 with both regular sonar and DV. Great unit.
https://www.raymarine.com/dragonfly/dragonfly4pro/This winter I picked up a Garmin Striker 4 to use for both ice fishing and on my kayaks. I'm no expert but many online have said that it's the industry leader at it's price point, which is a little below the Hummingbird you're considering. Fair warning, it comes in multiple versions and I may be confusing reviews of the more advance versions with my basic model. I was very happy with it on the ice but haven't used it with the kayak yet. It's got GPS built in, making it easy to mark structure, humps, etc.
https://www.cabelas.com/product/GARMIN-STRIKER-PLUS/2646072.uts?slotId=1http://fishfindersadvisor.com//?s=striker+4&x=0&y=0http://fishfindersadvisor.com/piranhamax-4-di/Up to now, I've been hesitant to put a finder on a kayak. To me even a bare bones kayak already has lots of places for your line to get caught on, especially when fly fishing, but figured I'd give it a try.
Good luck with your research.