I love mine b/c I use it so often on brew day. If you usually brew with a similar amount of grain, you can easily estimate the progress of the mash conversion. Once the Brix hits that point and stops increasing, you know conversion is largely done.
And especially measuring pre-boil gravity and progress of the boil-down. And the final runnings to see how efficiently you sparged.
To make it easier to take samples, WMT has a four-pack of s/s condiment cups for 94 cents. They work great for taking tiny samples and the s/s cools the wort very quickly. Just drip some wort into the cup and let it cool before using.