What is actually different?
Sage has been doing UK compliance longer than most of its competitors have existed, and that shows most clearly in payroll — the awkward cases, the historical corrections, the things that only matter once a year and matter enormously then.
Bizzle runs payroll too, in the same system as the books, billed per payslip rather than per employee. That is simpler and cheaper for a small team, and it is not as deep as Sage for a complicated one.
Outside payroll the comparison is the familiar one: Sage is accounting software, Bizzle is the whole back office including the phone, the chasing and the filing.