It’s basically a rapid prototyping tool that allows to get a fully functional plugin from an algorithm within minutes (or hours or days, depending on the complexity of the algorithm…) without writing a single line of code. The GUI and the VST interface is implemented using JUCE.
The light version (limited to 1 input and 1 output) is free.
Well, it’s as fast as you and Simulink make it… Think of it as regular C code. Basically, each Simulink block is transformed into nicely written code, but there’s some overhead due to the block-based structure, data logging infrastructure, etc.
In fact, the performance depends very much on the way you design your model. I recently implemented a sequencer + 3-voice FM synthesizer, and by simply optimizing my Simulink model (mainly by using vector data types and single precision floats), I could cut the processing time by about 75%. Now the Windows task manager CPU usage oscillates between 0% and 1% when it runs…