The built-in ballpoint pen is rather more a gimmick, but it works properly.
When two devices the pen did not work: in my Gigaset tablet and on my LG G2. As well as other display pins do not function. Did it have only mentioned here, because this is as good as ever on the displays when a pen so time does not function. In my Samsung, Sony and Acer devices on the other hand there are no problems.
Conclusion: nice pen, very good workmanship and everything is working properly. My tip is to write own little too thick, but for general operation, especially on the tablet, a pen is very convenient.