You might have heard that they do the same job since they are both solvents but each product is made for a different purpose.
The brake cleaner has a stronger cleaning power than the degreaser and it is designed to get rid of oils, dirt, grease or brake fluid when checking or repairing the brake system. While the break cleaner instantly removes the oil from the surface, the engine cleaner takes some minutes to soak in and then it needs to be hosed off or wiped away with a cloth.
In addition, the brake cleaner is mainly recommended for use on the brakes or other unpainted metallic surfaces and it can damage delicate plastic and rubber parts of the engine. It also evaporates quickly since it contains alcohol and dries instantly, leaving a spotless free of residue finish.
Apart from cleaning the brakes, car detailers often use it to spot where an engine oil leak comes from and to quickly remove oil stains from the driveway.
Depending on the brand, break cleaners may cost a little more than degreasers.