Just took the time to scroll through the various countries. Europe is well represented, so anyone wishing to watch UK, Irish, French, German, Italian, Swiss, Portuguese etc. channels outside Europe should be happy with what is on offer. UK selection is quite good and not a few premium channels to boot.
A mixed bag for the US. Many streams don't work or were poorly chosen, e.g. several premium channels are from Mexico in Spanish.
Only four uninteresting channels for Austalia, a country that is indeed hard to find functioning streams for.
Most streams are of acceptable video quality, but few in HD as far as I can tell. Most channels connect, though often only after 20 seconds or so.
While this app is offered officially by Amazon I am not sure of its legality, which is why the relatively low cost and non-obligatory nature of subscription is a good thing, just in case it is at some point removed for whatever reason.