What are the limitations of the results of a sensitivity analysis such as the one carried out in Example 6.1 (Greene plc)?

Data from Example 6.1

Greene plc has the opportunity to invest in a machine for the manufacture of a new product,
the demand for which is estimated to be 5,000 units a year for five years. The business has
made the following best estimates about the decision:
● The machine is estimated to cost £50,000 (payable immediately) and to have no residual
value.
● The selling price per unit is planned to be £10.
● Labour and material costs are estimated to be £4 and £3 per unit, respectively.
● Overhead costs are not expected to be affected by the decision.
● The cost of capital for such a project is estimated to be 10 per cent p.a.
● The project is not expected to require any additional working capital.
● In the interests of simplicity, taxation will be ignored.
● Assume, also in the interests of simplicity, that all cash flows occur at year-ends.
(a) Assess the project (using NPV) on the basis of the above estimates.
(b) Carry out a sensitivity analysis of the above estimates.