I am currently making a 2 wheeled SLAM robot that will use an array of either ultrasonic or sharp IR sensors with a particle filter. I also have a MPU-6050 and GY-271 and i am looking to turn it into an AHRS. However, considering that the map is going to be on a 2-D plane, do i really need a full AHRS? Can i not just use a magnetometer to create a compass for rotation readings?
AHRS will yield roll, pitch and yaw values. In your case, you would only need the yaw reading.
You could use just the magnetometer for yaw or rotation headings, but I would not recommend it. This is because the magnetometer is susceptible to magnetic interference. If the sensor is mounted on a chassis nearby ferrous metal, this also could be a source of problem. In this case, you would have to cover it with a magnetic shielding material.
For your information, there are algorithms like complementary filter, EKF and DCM that you could use to obtain the yaw value.