Yep, I have had good results with it, the hard part is thinking "negative" when making the shell and chuck.
Depending on the complexity of the box, it can become time consuming, but it sure beets $3,000.00 - $5,000.00 for a single run from a fabricator. Plus if it is a proto-type, it gives a fabricator an actual part for them to duplicate. It saves them a little bit of time, and you a little bit of money.