Best avoided! Charles Abby look only after their own interest against both those of the landlord and the tenant, and aren't very good at that even.
You can only expect a lot of empty talk, no service whatsoever, they expect you to chase up their so called engineers yourself for months, no common sense refurbishments whatsoever...
In other words, they are taking full advantage of this as a legalised form of scamming people, so little wonder they are apparently losing customers left and right and barely surviving at the moment.
Don't buy their "local company for better service" BS, and if you are unlucky enough to already deal with them for any reason, make sure they confirm whatever empty promises they make in writing.