This photo shows the old Teflon flax packing with the "miracle clay" and the new GTU packing. GTU is a knock off of Gore GFO, but it frays worse due to the braid design.
I used the Gore GFO for half a season on our new boat before switching to a PSS again. The Gore is the best of the flax type packings in terms of heat dissipation but it is at the very, very top of the galvanic scale, which can cause other issues.
These packings also needs a few drips per minute to run cool and not damage the shaft. My one complaint with this GTU packing, made by Western Pacific Trading and sold through West Marine, is that it tends to fray easily and does not make the cleanest cuts even when using a brand new razor blade.