OK, the 0350 has S30V steel, and so it will hold an edge slightly longer, but also will be harder to resharpen. the 154CM of the 0200sharpens pretty easy in comparison, but will not hold an edge quite as long. the 0350 is smaller, thinner overall, and has a thinner blade, but weighs less. the 0200 has BIG 3D machined G10 scales, which are really comfortable if you have large hands, but is thicker, wider, takes up more pocket space, and is heavier than the 0350. the thicker blade lets it take slightly more abuse, but the difference will probably be negligible. it is significantly longer than the 0350.
Overall, the steels and handles are close enough so that I would say that I would go for the 0350 if i wanted smaller and lighter, and the 0200 if i wanted longer and beefier. just my opinion.
As to assisted opening, AO is just a spring or torsion bar inside the knife that puts force on the blade when it is opened a certain amount. the protrusion is called a flipper, and it allows the user to flip the knife with their index finger. it is one of the top 3 preferred opening methods, along with the thumbstud and the spyderhole.