Yeah, it’s worth hanging onto them because as you said, you never know if you might have a use for them again.
The problem with a SET as isn’t just low impedance, but severe swings/spikes in the impedance.
Even though the above pertains to the Triode Master, it is still useful as the plot to the M3 Turbo S would look quite similar except instead of bottoming out at 16 ohms, it bottoms out at 3 ohms. That first peak around 30 Hz at 95 ohms is followed by another peak around 1.5 KHz which literally is off the charts! At 3 kHz the impedance is still over 50 ohms. Depending on how one uses the Speltz autoformers, they will amplify those peaks by a factor of 2x, 3x, or 4x, which only makes a difficult load all the more difficult. SET amps need not apply.