Mental Health Nursing - Undergraduate v Accelerated

I've recently graduated with a psychology degree and now looking to go back to university and study mental health nursing. I've seen that instead of the undergraduate nursing degree you can do an accelerated course or postgraduate diploma in nursing (if you have a relevant degree). I was wondering what difference is the accelerated courses compared to the undergrad course? And what advantage does it gain - is it worth doing the accelerated course?

Any experiences that you have or anything that will help will be appreciated!!