ISA or high savings account? (UK Specific)?

[bikerchris]

I have saved a few thousand pounds and it's currently in an poor earning ISA. I'm been looking on the excellent moneysavingexpert.com and it seems I have two options (best rates):

6.25% AER ISA with Barclays

OR

Kaupthing Edge offers 7.15% Gross/AER.

NOW THE QUESTION, if I'm on a 20% tax band, taking 20% off 7.15 =
5.72. So this does make the ISA (tax free) more favourable.

Is this right? Sorry, maths has never been my strong point, but I just want to avoid reading too much!
Errrr....anyone?