Hi,
I was a part time master student (coursework) and at the same time working as engineer. For me master class is just as degree class with the scope wide a little.
The benefit of taking coursework while working is that what you learn is what you apply daily during your daily job.
The only downside is that time management, really need to spend most of my time with assignment etc. This will become worst during thesis where more time need to be allocate for research and data collection etc.