How can you ever trust it? If you type text on someone elses keyboard; how can you ever know that it's NOT recording every key you press and transmit it to some third party? How can you know it's NOT secretly making a copy of all your personal data?

And what's the benefit? People have already been carrying personal computers around for more than a decade; we call them mobile phones. They fit in a pocket. Trying to borrow some random hardware instead of having your own hardware would provide which benefit(s) precisely?