You can do better than one backup razor, Techs are almost as cheap as dirt.
You're close; Don't forget to factor in age.This. According to my detailed calculations, you will need 87 Tech's to endure adequate backup.
That's one of my favorite combos as well.View attachment 478109
Love Techs. They are my everyday razor. Add an 80mm Bulldog barrel and it's shaving Satori.
I'm another big Tech fan. It is the only razor that I picked up a spare for. My son tried all of my razors and a pre-war Fat Handled Tech was his favorite, so now there is a third Tech in the house. The fact that they are a great razor for those new to DEs makes many write them off if they are experienced. I was one who made that error. Mine sat in a drawer for a year under the mistaken assumption that it was a beginner's razor. When I retried it after I had good technique, I was surprised when I ended up with an effortless, comfortable BBS shave. It is a great "beginner's razor", but it is, more importantly, an excellent razor overall!