YotaPhone and Pocketbook Cover Reader, which one you prefer to have?

YotaPhone and Pocketbook Cover Reader, which one you prefer to have? It seems that the YotaPhone is a phone with two screens,front screen is a normal HD screen, and the back is an E-ink screen, will be useful when you read books. And for the Pocketbook Cover Reader is basically a second screen for the Samsung Galaxy S4. Then, which one you prefer to have?