When evaluating a small film blowing machine, you must prioritize the screw diameter (typically 30mm to 50mm) and the L/D ratio (Length-to-Diameter), which should ideally be 28:1 or 30:1 to ensure superior plasticization. Additionally, check the die head design; a spiral mandrel die head is preferred for uniform film thickness. Ensure the machine supports the specific materials you intend to use, such as LDPE, HDPE, or LLDPE, and verify the maximum folding width of the film to match your production requirements.