So I recently started using a saftey razor that I purchased at The art of Shaving and they refered me to this site to purchase blades. I purchased the everything sample pack, my question is How many shaves is average for these blades? Also I noticed on the Astras that there are numbers in the lower corner of the blades, does this meen that I can or should flip these blades around and rotate thru the numbers??Thanks for the help