Product works great! I broke a small #8-40 tap in the hole and was able to rotate the center of the tap so it could be removed and the thread saved. Ball end mills are great for this and they are perfect for small holes and taps.
Pros
GENERAL USE - Carbon Steel (~HB225), Alloy Steel (HB225~325), Pre-Hardened Steel (HRC30~40), Hardened Steel (HRC40~45) and Cast Iron