I only noticed this thread when I started to look this part of the forum. Sorry if I am answering a question that has already been answered and reviving a zombie thread at this point.
In fact I am using the Instax mini for my moleskine travel journal and so far, it's fantastic combo! Be sure to decide on a book size that can accomodate the instax mini and enough room to write in it as well. For me, it's just right for both instax mini and instax wide! I love both of these formats!