Humminbird recommends you run your power directly to the battery, not through the fuse block. This is because they are very sensitive to voltage drops. When I originally installed mine, I had problems with the unit cutting out when I turned on the aerator, lights, etc. Called Humminbird and that was their suggested fix. Of course, if you do this, remember to install an inline fuse.
The problem isn’t wiring to the fuse block itself IF the block is properly installed with appropriately sized input leads from the battery.
The problems almost always arise when people try to use undersized wire from the fuse block itself or they try to tap into existing circuits that contain undersized wire for the load or have other active loads on the circuit. The resistance of the fuse block and the connections has to be taken into account when sizing wire.
Almost all freshwater boats contain hopelessly undersized wire that may meet the bare minimum spec (if a spec exists), but that is all. Basically, it’s cheap, cheap, cheap. I’ve replaced factory bilge and livewell pumps that were installed using 18 gauge wire which, while it will make the pump operate, is grossly undersized for achieving proper rated performance.
So yes, wiring to the battery is the “win ugly” solution, but as you say the problem is that many will fail to add the required inline fuse, which can make bad things happen down the road.
Grouse