It's mainly designed for people with mobile data packages on the iPad and iPhone, if you haven't got to worry about data limits and only use wifi there isn't much point to having it.
I only got it for my iPhone as I was going over my data allowance on my tariff every month. Since getting the App I hardly ever go over. Since getting it tho I always use it when I'm on my phone now as I find it better to use than a browser as the text comes up at a decent size and I don't need to zoom in etc (obviously not a problem with an iPad).
The only downsides I can think of is that you have to remember the codes for the emoticons and multi quoting or snipping quotes can be a pain.