The interface is as good as Intro to Math and it has a good set of activities for the sandpaper letters work. However, my childs school teaches with the cursive alphabet, so an option to use that would be much more helpful for me to reinforce the movement needed.
That being said, my son seems more willing to spend a bit of time with the letters on my iPad than he is at school - could be a case of fewer options for work over the summer or that it just takes less time to put the work away when he is done - regardless it is a well done app that my son enjoys using.
MHBurts about Montessorium: Intro to Letters