You can try out the harpejji virtually by using the Mobile Harpejji iPad app developed by Luiz H. Fonseca.
Click here for the FREE version of the Harpejji Mobile iPad app in the Apple App Store.
Click here for the FULL version of the Harpejji Mobile iPad app.
Here is a video review of the Harpejji Mobile iPad app:
Note that the harpejji app is currently only available for the iPad – iPhone and Android versions are currently not available.