I think that the rotation speed is stable, and performance against price is satisfactory product. Actually, in my work tool is only expendable item, so in 3 months or so the firepower drops and you can not make satisfactory products. Then, products that can perform stable work for a certain period at low cost are more helpful. Even if it is high, products that lose fire even if they last long will not make sense in my work. Purchase this time is a test-like thing but I think that it seems to be satisfactory tool.