Would I spend good money on Shimano brand oil for my brakes? Yes, because it's designed for what it's used for. Right tool for the job. Stopping power shouldn't be where you skimp.
As a side note, I'm not sure about Shimano's mineral oil, maybe it's a synthetic or has special additives, but general mineral oil isn't all that special. It's just a by-product of the distillation of crude oil to make gasoline. Also, commonly known as baby oil (mineral oil with fufu flower scent) and standard mineral oil is available at any drug store for pretty cheap. It's just a non-compressible fluid. In reality, any fluid will work, even water. The only real reason brake fluid is used in cars is because of the reduced expansion, scortching, and bubbling when cooled/heated to extremes and it doesn't gel up when cold . Will bike brakes heat up as much as car brakes? Not under normal use, and probably the reason mineral oil works fine.
