My personal experience
While Image Magic prints quickly and their website is super easy to use, I am overall not really happy with the print quality of my product. The colours on my original work and the printed product is very very different. My postcards ended up turning out far darker than it looks. It's possible that the artwork I sent in wasn't tweaked properly (though it looked fine on my screen and my phone, even when viewing in CMYK colour profiles). So I would say that this is something you should keep in mind.