Originally Posted by
veganbikes
They may not work every single time but if you know how to use the tool, it is less likely to be an issue. A lot of people end up not doing it right and having issues. Pick one spot on your rim and use that spot each direction you are aligning in so you have a much much better chance of fixing the problem.
Yes, I'm sure it works many times. But I think it is good to know that, apart from possible wrong manufacturing of some tools, it may happen that 2 similar derailleurs, otherwise of very good quality, may need different alignments of the hanger in order to work properly. I guess it is the case for derailleurs that happens to be manufactured at the opposite limits of alignment tolerances, or maybe out of the tolerance. For such cases (not many, I assume), the only solution is visual alignment of the hanger. This might lead to very good results, otherwise not possible with the tool.