Do your maths. Only costs in if you average >1200 miles per month off of your home charger vs the ~2.5p/mile a 7.5p/unit off peak tariff gets you.
It doesn't say anything about public charging being included in this monthly fee.
Basically if you live >30 miles from your 5day a week place of work AND don't need public charging to get home again, it works. (Ignoring weekend driving)
Also these Smart tariffs usually have your charging switch on and off during that off peak period increasing the number of cycles of the relays / contactors by probably 4 to 6 times.