More so than the others, this guest book has more... commitment involved with it, {oh the irony ;) } ... it potentially has 'lasting' guest book status and could become a permanent feature in your home.
To call it a guest book is perhaps a little limiting, it is, after all a tree... if I had one of these I would put it in a conservatory { after the wedding } and when 'guests' visit my house I would ask them to 'leaf' more notes {sign and dating too}.
I have a 'house' guest book that I get everyone to sign and leave a message when they visit, especially those people who I don't see often or perhaps will only ever visit my house once in a lifetime.
This 'Tree Guest Book' would be ideal for that...
I would suggest maybe making it on a piece of plywood - or something transportable, particularly for the wedding but also incase you move house during your lifetime. And I would also consider having the 'leaves' made from something durable {but replicable, so you can easily get more} so they last the test of time.