I've been wanting to get into these games/books. What is the average length of one in terms of hours? Also is there a good Tin Man Games book to start with?
I'd still recommend An Assassin in Orlandes as a first Tin Man game - it's a good introductory book to the Gamebook Adventure series. As for number of hours, it's hard to say - time will be longer if you don't use bookmarks and/or spend the time to find all the out-of-the-way things (which are kept track of in the menu for you.)
They're superb I dont know about anywhere else but back in the 80's the Fighting Fantasy gamebooks were HUGE in the UK. Parents loved them as their kids loved reading books ! Now to have many of the classics on iOS is a dream. I prefer the Fighting Fantasy books but their own ones they did before they got the FF license are very good. Well worth picking up