Material: Check if the machine is made of high-quality and durable materials, are the forming rollers made from 45# steel, GCr15 or Cr12? Normally Cr12 hardness is the best and good for roll forming hard strength steel coil, but the material cost is highest, too.
Precision: You can compare the purlin straight or not, hole punching precision and cutting precision, also, purlin surface effect..
Warranty and support: Check if the machine comes with a warranty and if the manufacturer provides reliable customer support for any potential issues or inquiries.