OpenSTA is an exellent tool for load and performance testing. It is definitely not a tool designed for functional regression testing. However, u can add some response verifications to your code and verify excpected html is returned. therefore you could use it for some forms of regression testing. If your main goal is to load type testing, but u also want to use your same code base to do some light regression tests, it would be a good choice. For pure functional regression stuff, you might want to look elsewhere.