Style Cartel is a little bit lighter and more blue-toned than Ryan. Ryan is such a deep shade of navy that it almost looks black in lots of lighting.
Don't mind the airbubbles on my ring finger! Or the bright blue glare, which is from my lamp and its blue shade.
Overall, I like Ryan more than Style Cartel. Ryan's formula is dense and highly pigmented. It can almost be a one-coater, as long as you have a steady hand. I did use two coats in these photos, mainly to help neaten the line around my cuticles. Style Cartel, however, is much thinner, almost the the point that it's watery. I left it at two coats on my middle finger, and did three coats on my pinkie. You can see that the third coat deepened the shade just a little bit, but it still looks lighter and bluer than Ryan.
So, Do I Need Them All? Ehhhh, I would say no. They are slightly different, so I wouldn't call them dupes, but they're so close that I don't think owning both is a must. My personal recommendation is Ryan, simply because the formula is so much smoother and more opaque, but Style Cartel is also a good navy blue polish.