I'm still learning Instax. I bought a Mini camera and have not quite finished a single pack (I'm not very impressed by the B&W material, BTW), and I've only started on the second pack in my LomoGraflok. I want to like it -- it's got better color than modern Polaroid, IMO; in fact, it reminds me very much of Kodak instant film from the 1970s/1980s (not surprisingly, it's my understanding the process was co-created by the two companies). I've even bought (so far) two old Kodak instant cameras and an adapter to put Instax Square in those -- though at present the one with metal gears won't expose and the other one that does expose has crumbled gears). I'll try that again, most likely.
For subject matter, it's pretty much a snapshot material, IMO. I've seen some very good images done on Instax, but few done with the Fuji camera -- Mint, various adapters, and single-sheet (labor intensive, too much work for me) let you get a better lens involved.