What's not to like about this item? This chain wear indicator provides a very precise idea of how much wear one's chain has. In this way, one can easily gauge when his or her chain needs to be replaced, which can end up saving a lot of money in cassette replacement down the road.
The Park Tool chain wear indicator is more expensive than other off-brand chain wear indicators on 鶹, but in my opinion this one is worth the added expense. Most wear indicators on 鶹 test for a chain stretch of either 0.75 or 1%, but this one from Park Tool checks for 0.5 or 0.75% stretch instead. The 0.5% measurement is especially useful for chains that are designed for cassettes with more than 10 cogs, which includes a lot of road bikes. Unless one primarily rides something like a single-speed bike, the Park Tool is way more versatile.