For a great introduction to Tangent Control Surfaces why not try out the Apps for iOS and Android
The element-Vs is a fully featured set of Element panels in the form of a tablet app. The virtual versions of each of the Element panels have exactly the same controls and layouts as the real thing so you won't be missing any features.
Standalone or combine
You don't need to own the real panels in order to use the app – it's fully standalone. You can combine it with your real panels to expand your Element set, using it to replace panels in the range that you don't have. Or, if you want to add another panel to your range, say for example you would like an additional Bt panel, then you can use the app to do just that*.
*This requires the host application to support the Tangent Mapper.
Supports most tablets
There's an iOS and Android version of the app covering most tablets – all generation iPads and any Android with 7" screen size and above.
Create a totally "glass" control surface by using multiple tablets. As long as all your tablets are linked to the same Apple or Android account then you only need to buy one copy of the app.
A free version of the app is available which allows you to try the app before buying it. The free version is fully featured so you get to use every aspect of the app, the only limitation being that you can only use it for a total of an hour in any day.
Sitting at the back of your suite with your client reviewing a grade.