From the author's pov, it's an interesting proposition. Take sorcery for example: http://www.amazon.com/s/ref=nb_sb_noss?url=search-alias%3Dba...

I bought this and played it for about an hour to completion. For my hour, I'd have made them $0.12. Instead, I paid $4.64.

So for them to get to the same profit using this model, they'd have to attract $4.62/$0.12 = 38 times more users. i.e instead of having 1000+ downloads, they'd need to be in the 38k+ downloads range and for everyone to have played it to completion.

I see two problems for this particular game. 1. Fighting fantasy based games are a niche market so is there going to be a large enough user base to support this? 2. I'd say that the length of a typical gamebook shouldn't be more than 1-2 hours as it will get very complex. So they're kind of capped re per player usage.

Since it's a niche market, I don't imagine there would be hundreds of thousands of people trying this out for 5 minutes each.