Roller is funny. The method of Roller is that each letter rotates (optionally with different speed) around its center. Rotation is not enough in itself, because if all letters would start from the same angle, then there would be a phase when the complete solution is visible. That's why all letters start rotation from a random angle. The disadvantage of Roller is that the animated gif images could grow big in kilobytes if the angle speeds are different.
The weapon of this CAPTCHA: The method is to obfuscate the enemy. In all the frames of the animation the letters show up in a different angle.