I'm also a fan of the HDI. It's great to be able to check hollow depths to match someone's old hollow (if they don't know what it was). The only negatives are the price (if you are a home sharpener) and it's a bit cumbersome to check a blade while still on the clamp/holder. The blademaster quick square is also a great tool and will give you the same result. As a side note, I checked a skate that was FBV sharpened with the HDI and I got a depth of almost 0.002". I was under the impression that the depths were all under 0.001". It was on a Tuuk LS2, maybe they tested it with a narrower blade.