Regarding metal toothpaste tubes- they used to all be metal. People used to fold/roll them up as they used them. A brand advertised for adults, Vote, was the first to use plastic tubes.
OK, so I’m late with this. Oh well.
I don’t get six months per cartridge, but an 8 pack will last me a year easy - shaving 5 days a week. So 6 weeks/30 shaves per blade works for me.
Actually, that was for making very fine adjustments to the angle of the blade giving you a more, or less, aggressive razor.
CMC fnord!