You'll notice on the higher end versions (like Abbey Bike Tools HAG) the top is a harder metal -- here it's all aluminum, which if you aren't super careful with the threads can cause some issues -- which for alignment is not something you want, even off by a little bit makes a huge difference. Read more

The tool can be adjusted to be square with the derailleur hanger and can be used to measure along 360 degrees of the wheel's rotation plane without moving the gauge rod back and forth. This was all very appealing to me at the beginning. The problem is that such an operation is achieved with continuous adjustment of the retaining screw at the top, which secures the hanger bolt to the long arm. As a result, the canal / groove which accepts the screw is gradually deformed and eventually damaged. This happens because the material of the tool is soft aluminum and the screw inevitably digs into the body of the bolt while applying the force necessary for unbending the derailleur hanger. Afterwards, squaring of the tool becomes nearly impossible due to the uneven surface of the canal. It is difficult to work with this tool and its durability is very low. I initiated a return after the first use and purchased another tool. Read more