The Valet Autostrop safety razor (1906-1946) must be one of the most 'sustainable' safety razors that were ever made, it was designed with a replaceable blade system that obviously had no plastic in it, but wait for it.....you could also strop/hone your 'disposable blades' with a small leather strop when they become dull, extending their use well beyond that of its normal life expectancy, even as long as a year or longer on a single blade! These razors have a cool steam punk design about them that was also functional and certainly made to last, the tray of this razor is made from solid 1.2 mm brass, for crying out loud, carports nowadays are made from shoddy 0.35 mm sheeting!
The problem with most of these razors is that the leather strops have deteriorated to such an extent that they are no longer useable, however it is fairly easy to make one if you can get your hands on some 1.6 mm leather. Most folks will probably opt for simply replacing the blades when needed, as they are quite cheap compared to cartridge system blades. I am yet to use a stainless blade in this razor, but I got an average shave from the carbon steel blades, the razor works very well and I think I am going to have a new love affair with these razors when I get the blade selection all sorted out.