DanQRI have ordered 7 Kershaw Knives from Massdrop, all of which passed through customs without issue. These knives use a torsion bar for assisted opening.
Taken from Kershaw's website:
"Unlike a switchblade, SpeedSafe® blades DO NOT deploy with the push of a button in the handle or by gravity alone. Instead, the user must overcome the torsion bar's resistance in order to engage the SpeedSafe® system."