There is nothing illegal about an IFR aircraft, in this case a Cat B aircraft descending below the circling MDA to 300 ft agl during daylight hours in VMC if they can maintain visual clearance from obstacles within the circling area and maintain visual contact with the runway and/or runway environment. It’s clearly laid out in the AIP.
Its not VMC its visual; 250ft is not 300ft and if you were familiar with MB circling it is an issue in VMC.