My dd is also 'reading' these books.
IMHO a good mix of mainly free range (children's lit) and some battery books (reading schemes) is always advisable.
I think these 'no words ones' get children into the 'ORT' way of thinking. So when the words appear on the next stage they 'get' the characters, setting, their own biases as a reader and an expectation that basically the plot is likely to be something like:
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everything will be great
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until Floppy/Dad/Kipper mucks it up
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and then everyone laughs on the last page (that usually has the words 'Oh no!')!!!
This later empowers the reader to really focus on reading the words using all the techniques they possibly can. They now know the other text features so well they can draw on a vast comprehension of the overall texts to 'work out' what an unknown word might be.
IMHO (again) This scheme is particularly good for children who do not have parents who read with them at home because they are so very very accesible!
The down side of them is that children who love literature, because they have always been read to, may actually find these books a little dull as in nature they do lack depth and variety(to begin with there is very litle variety and later I would argue no true variety).
So, like piscesmoon suggested we must make sure we are asking such children high quality and varied questions about the pictures (I also love the post-it ideas) as well as, of course, continuing in our reading of vast quantities of other high quality childrens picture books with them!