I came up with a powder check a couple of years ago and have been using it ever since. It cost me nothing out of pocket.
With each block of 50 loaded cases, I just use a short length wooden dowel that will slide into the case easily, and hold it in such a way that one fingertip just touches the rim of the case, and go down the rows.
The method is surprisingly sensitive. I caught two loads that felt a bit under. On the scale, they came out 0.1 grains low. But I really use it just to check that each case has about the right amount of powder in it, not no powder or a double charge.
Even though I'm an illustrator, and therefore a very visual guy, I like this method because it brings anther sense into play, touch.