Section 6. Bonds or notes issued by the agency and their transfer and their interest or income, including any profit on the sale thereof, and the improvements belonging to the public facilities' owner shall at all times be exempt from taxation within the commonwealth; provided, however, that nothing in this chapter shall limit or restrict the ability of the commonwealth or the municipality to otherwise tax the individuals and companies or their real or personal property or any person living or business operating within the boundaries of the development zone.