The big thing nobody is mentioning here is mapping. You had better do your homework for your area if you are thinking about Garmin. You are stuck with their maps good or bad at this time. This is especially true if your lakes aren't MaxDef Garmin scanned. Their nomenclature is tricky but if they didn't scan it I would be skeptical. Lake Barkley is my home lake which is a pretty big one for bass people and is supposedly Hd but is dreadful. No way their staff guys are ledge fishing with Garmin maps on Barkley.
All that said though I got into the units cheap and run Lakemaster on my phone when I need it. As far as doing what is necessary to catch crappie sonar wise it is solid and I have owned Hbird core series and spent a fair amount of time in Lowrance boats and don't feel handicapped in the slightest. I guess I am in the minority in that opinion, but I am strictly basing my opinion off the ability of the Si, Di, and sonar giving me the information necessary to catch fish. If your into taking pictures I would say you will be disappointed with the Garmin with either transducer and ought to get the Mega. But I would have to spend some time in the boat with one to see if they improved some things over the core series before I forked over that kind of money.
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2018 Crappie Masters Kentucky/Tennessee State Champion