While that Canon printer gives impressive looking results, it is hardly portable in the way the SP-1 is. I can put the Fuji printer in a jacket pocket. And I can hold it in one hand (or even have the opening sticking out of my pocket) for it to operate. I don't have to put it on the ground, a table etc to use. Plus, it's not all about image quality, but the joy that comes to people's faces when they watch the print develop in front of their eyes.
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Yup, no question the Canon is larger than the Instax, definitely not pocketable (unless you're wearing a coat with those 'saddlebag' pockets
🙂 ), but it does fit perfectly into my Tenba Small Messenger bag, along with my camera body with three lenses. Additionally, the Selphy will work with any camera that takes an SD card, so if you have other cameras besides a Fuji, it will work with them too (the USB connection is also a plus). And to watch the manner in which the Selphy prints (dye-sub, so it lays the image down in the the 4 layers of color) is pretty magical too.
Here again, I thought the SP-1 was a great idea and complement for the X100T (which I also have and love), but after having used it for a month, it just didn't add up for me. Ultimately, I chose to carry a bit more bulk for a larger and better quality print.
I think the other thing that got me, as I recall, was the cost -- when I bought the SP-1 two years ago, it was $172 (I've since seen it for $129 at B&H). The current replacement for the CP910 is the CP1200 at $99.99 (with the battery adapter it pushes the price to $148.99). But then the paper/ink prices are a bit different -- 54 sheets with the corresponding ink cartridge for the Selphy is $17.99, for the SP-1 it's $12.28 for 20 shots. In the long run, I couldn't see the extra cost for the Fuji instant film/paper as being worth it, particularly when compared to a printer that can produce larger prints with (as I personally see it) better image quality.
So I guess it all comes down to what's important to you -- if the small and pocketable size of the SP-1 is important, then it's an attractive option. But if you're willing to sacrifice the printer's pocketability for a larger and (maybe) better print quality - and save money over the long haul on the print materials - then the Selphy may be one to check out.