It's highly readable and I could (have not other things got in the way) have read it in one session. There is so much potential in this scenario that it's inevitable the authors will end up surprising the reader as they take the story in unexpected directions. After finishing it I kept wanting to ask the authors about several things which occurred to me.
There's the (in)convenience that iron won't cross into another world with severe limiting effect (never mind that you can't take more than you can carry). This makes industrialisation exploitation very difficult. This is never explained but it suits the purposes of their story. Do they have a logical reason behind it?
The result of all this is that akin to a pioneering frontier type lifestyle similar to that of the colonisation of America only without the Native Americans. Some way into the story we learn that a fifth of the world's population have stepped over. Really? A fifth (or more -see a following point) of affluent societies have forgone their comfortable lifestyle to become pioneers. Sorry, but I for one like the creature comforts of a high tech society.
Also, while I know it's set a little way in the future and the device is relatively cheap. It would be difficult for those who would really need it to get their hands on it. I'm thinking of the majority of Africans who suffer from famine and oppression and lack of education. How could they get their hands on the electronics needed? Come to that, how could they get their hands on a potato?
None of this affects the story, it's just stuff that I thought of as a result of the story and doubtless there are numerous more implications or omissions to be found. This is actually another reason why you should buy this book -it makes you think.
I started reading this around lunchtime and finished by early evening which tells you something about its readability. If you haven't read any of this series before, start with the first. But don't worry, it won't be long before you're reading this one. You won't be able to help yourself. Great fun series.
All right, Aaronovitch, when's the fourth one coming out you lazy sod?