I use Silver Spoons Royal Icing Sugar Here in the UK, it's not a ready to use mix you do need to add water, but that's it
So I find it really easy to use it does what I need it to do, I can make it to the consistence I would like then.
Saves me time making it from scratch too, especially when I sometimes don't have the extra time to do that.
Silver Spoon used to make the best chocolate chips too but they stopped making them still on the hunt for the perfect chocolate chips no luck so far & I have tried loads.