I have about 20 of these printed and left throughout my house. I like them because they are 1) one piece, print in place 2) have a big hole to attach to keys, carabiner 3) rugged 4) one-handed close. I have not had one of these break since I started printing them. I have remixed the original to add some needed fillets and chamfers in some sharp spots.

*** WARNING *** Razor Blades are extremely sharp. Please use caution when inserting the blade and when using it. I would use this design for light duty only.