After shooting a friends 365 xl with the flat trigger upgrade and liking the feel of the 90 degree break, I decided to install Sig’s version on my EDC. Since mine was the external safety model , I had “read between the lines” of the YouTube tutorials. It was a bit tedious but after watching the vids half-dozen times I managed to accomplish the task after three attempts. Very pleased with the results. If you are considering this upgrade , be sure to go over the videos several times prior to the work. I able to do it in spite of arthritis in hands/fingers and less than stellar vision. I’m very pleased with the result!