Light Emission Technologies LET F40T12 835 White De Luxe Fluorescent Tubes

This lovely pair of Chinese tubes was an unexpected gift from Daniel. Never in my entire existence would I have ever dreamed of having some of these because they were kind of a legend and I only ever thought that to have these I would have to buy a vase from ebay, but I was ever pleasantly surprised to have found these in the coffin! I love the super soft color and I love how crappy these tubes are made lol. They are shorted by couple millimeters and when they are installed I see large gap between endcap and socket. I wonder what is the lifespan of these tubes? I see that they have cathode shields and the filament seem to be double spiral so should have a moderate lifetime? Also Jonathan has told me a bit of lore regarding these tubes, that some of these have krypton filling like T8 does and some have argon filling. I suspect that one of my pair is krypton filled because it starts super hard and flickers like a madlamp. I also wonder are these tubes tsill available for purchase in GB?