Re: DOT 5.1 is it worth the extra £ ?
Not sure it is worth going specifically for that fluid, especially if you do not change your brake fluid that often.
A normal DOT 5.1 fluid might be cheaper (even Halfords DOT 5.1 is half the price of the ATE Super Blue / Super Gold), easier to get and may exceed the wet and dry boiling points.
If you want to spend silly money on brake fluid then check Castrol SRF. It has a higher dry boiling point although a lower wet boiling point. And is about double the price of the ATE stuff.
All the best