I bought this to troubleshoot lines out on the road, when you're not sure why a channel isn't working etc, i have since found even more uses: finding corresponding channels on a multi that isn't labeled for example!
The diagnosis of the faults aren't always 100% but if it says the line is all good then without fail so far, it has been right. To cut a long story short, i couldn't really do without it now. We sometimes even use this to silently line check before a show. and for the price... well its a no brainer for me. i shall now be purchasing the NL4 one as well!