Klever Kurve 10 Pack - Klever X Change Replacement Heads - Safety Cutter

This design seems to be most effective on opening cardboard boxes. It's not a perfect system for switching out blades, as the plastic tabs can be a bit sticky to operate, but, it's not bad. The blade is only on the inside edge, making this a safety design, so you are not likely to cut yourself/others with it by accident. This design also means you are far less likely to damage anything inside the box you are looking to open.

These replacement blade's are the best out of the 3 choices and most durable.

There is still protection from the blade even though it is thinner. My hand does not hurt after using this all day. There is less time struggling with box flaps.

do not work for a gut hook