For years I ran a handheld gps for trolling speed and mapping, along with a mid level eagle fishfinder.
When I designed my new boat I included a combo unit and I love it. I got a simrad go9 with cmap pro mapping. I link it to my iPhone and I can control it from my hand.
Its nice not to have to worry about batteries in the handheld and it’s convenient to have all the controls in the same place, but I can’t say I catch anymore fish with the fancier electronics.