Well, since obviously 50p per day is not the same as £5 per month, how does this actually work in practice? Is it 50p per day capped at £5 each month? I presume the facility is not intended to support long-term debt, and would be withdrawn if over-exploited.
If the 50p per day charge really applies when "any of it is in use", then this is most definitely *not* better than a credit card interest rate when the amount by which you overdraw is small.
Typically one might overdraw by only a small amount, for only a short time. Say it's £100 for a week. Then the charge at 50p/day would correspond to an uncompounded interest rate of 183% per year.