I have not done so yet but am planning to take the 25% TFS in the next few months.
The reason for doing so soon is to gift it to my heirs as a PET, and obviously the sooner I do so, the greater the chance of my surviving 7 years.
Even if I don't survive, the gifted sum will only be subject to 40% IHT at most, rather than IHT + income tax.