Bick one is a fairly aggressive cleaner. Bick 4 is a lighter cleaner as well as conditioner.
The 4 is all necessary for most.
Harley dealer nearby? This stuff has to be the same product as Bick 4.

Name: DSCN3631.jpg Views: 165 Size: 60.7 KB

I have several vintage strops. The Bick 4 keeps them like new, used once a year. Supple and clean.

JMO