There is a reason straight shaft is more expensive. All large companies use straight shaft trimmers. They are the easiest to use and most effecient
They cost more because of the gear reduction knuckle on the end that gives more torque to the head and changes the rotation of the head to counter clockwise that everyone forgets to put grease in.
If you could only own one string trimmer, would you choose a straight shaft or a curved shaft, and what are your reasons ?