This Olfa rotary cutter is my go to cutter when I am cutting a lot of fabric.  Squeezing the handle with your hand pushes the blade out ready to cut. Once you release your hand the blade retracts back into a safe position.
this rotart cutter has a comfortable grip ergonomic handle which helps reduce hand and wrist fatigue and accommodates both left handed or right handed users.
Features:
Comfortable grip ergonomic handle
Quick and easy blade change
Contoured handle for comfortable cutting
High-quality Japanese carbon tool steel
To protect surfaces and blades use with rotary self healing cutting mats.
Double-honed blade provides superior initial sharpness and edge retention.
CAUTION!!  The blade is extremely sharp, handle with great care.  Please keep out of reach of children.