Top-down using a controller thumb-stick for reference.
When using 8 direction behavior if you approach a solid (wall) at a 45° angle your angle of movement changes to be parallel to the wall in the relative direction you were heading and the speed remains constant.
When using the custom movement behavior (or bullet) with 360° of movement and you approach a solid wall depending on the direction of approach, the angle of movement appears to be parallel but the movement speed either increases, or decreases drastically depending on the angle of input.
For example if I approach a wall that is positioned vertically on the y axis at a 45° angle, and when I collide continue to maintain my input, my character moves at a higher movement speed than what is set. If i than rotate the thumb-stick towards the opposite end of the Y-Axis but still towards the wall on the X, the movement speed decreases and my character will not begin moving down the y axis until the stick is quite a way past the centre in the opposite direction. When fully moving the stick to the lowest point on the Y-axis, while still maintaining the contact with the wall, the max movement speed is greatly lower than what is set.
This happens with standard movement behaviors.