I've worked on this and also did cross-compilers for it. It's industry standard. It's not only used in cars, it's used all over industry control automation, airplanes, power plants, ... It's reliable and creates almost bug free code. It allows real-time control loops. It creates highly optimized C code (I wrote a C++ backend). You wouldn't want to do that in C or C++ by hand. Before Simulink my prev. company used Occam, a powerful Smalltalk/Objective C like language with CSP, which ended up being succeeded by Go.

But there are also many more such successful tools being used industrially, esp. from Siemens.

The biggest problem with it are diff tools. There exists a graphical diff in the toolbox, but I haven't seen it being integrated in its workflow yet.