Instruct: Classify an Amazon review into positive or negative sentiment.
Query: Be Careful!

This cartridge is supposed to be the same as LC51BK but it will not work in my Brother printer/fax. It does not recognize the cartridge. When I compare the "real" cartridge to this one I notice a difference: there is a little plastic pin that sticks out of the top of the "real" cartridge and is making contact with something inside the printer. The "comparable" cartridge looks exactly the same and fits in the slot perfectly, but does not have this little plastic piece so my printer is acting like the cartridge is not installed at all. BE CAREFUL and check your old cartridge before purchasing this one. It is a great deal but may not work for you!