I have pushed literally thousands of linear feet of putty in the process of window glazing, and have been using this putty knife for the last twenty years (yes, the same one).
If you really want the professional edge when glazing an old wood window then you need this tool. The bent blade allows you to point the putty exactly where it needs to be. With very little practice the tip of the blade becomes an extension of your index finger or thumb for exact setting and cutting of glazing putty.
Simple, cheap, highly effective and very satisfying. Means it’s a cool tool in my book!