Yes, a $600 unit does a better job but certainly better some info than nothing and since most people already have a smart phone it's free. It's silly to say you shouldn't check it occasionally if you have the ability.
Just like any other navigational device, it shouldn't be used to the exclusion of other available information most specifically, your eyes. Obviously, it's only good if you have cell coverage but if you are coastal cruising, that's 99% of the time and that is also when it is most useful. Especially for large commercial
ships, the lag time isn't a big issue unless you are trying to cut too close in front of them in the first place (I presume, you would actually look out the window to see where the ship is before cutting in front of them regardless of what the instruments say).