Expandable broadheads are very popular with a lot of bowhunters. The primary advantage of expandables, or mechanicals, is that they tend to fly more like your field points than fixed blade broadheads.

Many expandable broadheads use small rubber bands to hold the blades in place during flight. You should regularly check these bands for small nicks or cuts. You should even check new bands coming out of the package. Quite often, nicks or cuts can be found in brand-new bands.

Damaged or defective bands don't have the strength of uncompromised bands, and may break when shot out of a compound or crossbow.  Then, the blades will open during the flight of the arrow and change the point of impact. In other words, you'll miss, or even worse, make a poor hit on an animal.