The biggest difference is that a slow juicer slowly squeezes the juice out of fruits and vegetables, you get a nice juice. You throw away the pulp left in the machine. With a blender, a piece of fruit goes into the machine whole and you use it all. In addition, you can't juice hard vegetables or fruits with a blender. You beat an apple to a pulp with a blender and it doesn't really become a juice. And you can't get anything resembling juice out of a carrot or piece of ginger, either. You can, however, make other things with a blender such as milkshakes or smoothies, so it is multifunctional.
So the juice from a blender is generally a bit thicker and contains more fiber. This is because the pulp is not left behind with a blender, the slow juicer does not grind everything so because of this it is not in there. Because there is no pulp in the juice from the slow juicer you get a slightly thinner and clear juice. We also recommend with a slow juicer to make some crackers or muffins with it so you do get fiber without the pulp.