Probably not so much misunderstood, but in my opinion underrated are tools for pairwise (or all-pairs) testing. Over the years it has helped me a lot in coming up with a concise set of test cases, or strimming down bulky test sets, while keeping confidence in the coverage achieved.
One tool in this space which is my favourite is PICT from Microsoft. Very lightweight, and I like the fact you can use it from the command line.
If you want to learn more about pairwise testing, check out Venkat’s course on the MoT DOJO.