I'd like to add I own a few instax stuff and my favourite is the instax 10, the pictures are lighter and more vintage and you can set the flash OFF when you don't want it only flaw is the looks (ugly and fat compared to the instax 25), noisy, no timer.
Instax 7s is rubbish
Instax 25 is good looking but can't turn flash off although they is a self timer
I also have the instant back for the Diana F+ which is really fun especially since you can change lenses and use different flash. I use mine with the ringflash and the fisheye or super wide lens and the main advantage for the Diana F+ setup is that you can do multiple exposures with it as well as long exposures! A lot more fun! Disadvantage: not as compact?
I am now looking at the instant back for the LCA so.... there are plenty of people that still uses instax XD Just that they're not as pro looking