Carnival wifi worth it?

I have a question about the wifi. So I'm about to go on a cruise soon and was thinking of purchasing the wifi to read/reply emails. Is the only wifi plan if you purchase it for the whole week? Like is it possible just to pay for the days that you need it? It doesn't seem worth purchasing for the whole week when all I need is like 10-20 min a day of wifi. Also I know my ship has the FunHub, is that more worth my money?