As stated, your question is too general to answer with specific recommendations. SimBiology is certainly useful for certain kinds of biological models. But any problem you solve in SimBiology could also be solved in base MATLAB, although you would probably need to write more code, and it might not solve as quickly. Depending on exactly what you want to do, there may be other MathWorks products or free modules on the MathWorks file exchange that could be helpful. If you want more specific recommendations, I suggest you share more about what you want to do.