Unit test generation is the wrong way to perform unit testing. The proper way to do unit testing is to create test cases before you write functional code, then develop your code until the tests validate, this is know as TDD (Test Driven Development).
One of the key reasons unit test generation is a bad idea is because if there are any bugs in your existing code, the tests will be generated against those bugs, therefore if you fix them in the future, the bad tests will fail and you'll assume something is broken, when it's actually been fixed.
But since the code is written, it's now water under the bridge. And possible buggy unit tests are better than no unit tests at all. I've always preferred NUnit and there's a NUnit compatible test generator here (very affordable).
