It's bad, mate.
£41 for four hours of work! Two of those jobs per day = £82
But Groupon take their cut, so the actual received cost is far less; and there's no guarantee of repeat work at better prices.
I'd rather spend the time knocking on doors than working for that; I bet I could make more money, hour-for-hour spent door knocking and cleaning those new cleans, and have 'guaranteed' repeat work.