Normally they come with publicity some more invasive than not but they can still be very useful. Almost all of them are for free and some of them are surprisingly good like the one above for example. It is highly responsive and sounds good so if you are looking to incorporate some Chinese strings and percussion into your composition this is a good alternative. The only drawback is that it is based on only six notes which I guess is to conform to a more traditional Chinese sound. Still can be very useful if even two notes belong to the same scale as whatever composition you are working on...
In either case will try to report on more Virtual instruments that can be useful as I do like that almost any instrument exists as an application and can be used to inject some flavor limited in scope or not... Plus the hands on playing is more fun than sequencing notes!
The sound in the video has some glitches that I did not hear when using the application so it could be the fault of the video recording and not the app itself.