I have a batch of TF5 stock that is now about 4 years old. It still works. I tend to mix 1:9 for working and discard after 3 months, it turns gray, or it takes more than 45seconds to clear a test film. I use it for both film and paper. TF4 has its uses too for alt printing work and can yield a different color tone for salt prints and Moersch's Lobotype. I don't care for TF4 because of the fact it likes to separate. TF5 was the recommended fixer when using Pyrocat HD as the developer but I have used Ilford Rapid too with no issues. IF I walk into a camera store that sells DR supplies I always pick up fixer and FB paper and anything weird they might have.