It's probably pretty good if your mother tongue is something that is available, I can learn Spanish in English, but isn't that making things hard for no reason? Yes it is.
Since this is only "freemium" it should be compared to other paid services, which are presumably often better and involve a real teacher.
Most of what you can do for free is helping other people without learning a lot.
I actually read more and faster now that I have one.
PRO: it's small to bring along,
Great screen, as expected
Get books from wherever.
Remembers last page read
Good battery life
Change font size to read in dim light
CON: the browser, restriction on downloadable filetypes and links that open new windows don't work.
The text-to-speech voice sucks, this is 2011 computers should speak like us now.