I think they are great. My opinion is that if your child is engaged with words and pictures and a storyline, that is terrific. Whether they are turning pages or swiping a finger the important thing is that they are reading or being read to.
However, that being said . . . the other very, very important ingredient to those early literacy experiences is the intimacy. It is the togetherness, the reading to each other, the shared laughter. You want your young child to associate reading with closeness and warmth. So be sure to stick around. Don't just hand your child a device and assume she is self-sufficient. Share the book, maintain that closeness, read together.