Just check 2 things:
That your bank won't charge you (aithough on SVR they shouldn't)
Find out when they will apply your overpayments to your account to calculate interest. i.e. sometimes they don't check how much you've overpaid & therfore reduce your interest charge until the end of the year.
I know my bank doesn't care when in the month I pay 1st or last day is all the same to them so I pay on the last.