Not personally, but the one I saw on a boat several weeks ago, sure seemed to be BIG. Took up quite a bit of floor space. And this was for a boat with only one battery.
At best, they will provide somewhat of a very slow, and very moderate amount of charge to the batteries. Want more power, need bigger solar cells.
I would think it's a good idea if you're tournament fishing and on the water for 8 - 10 hours. Every little bit helps on a long day, been thinking about getting one myself.