Mira sport were very reliable, but basic shower units. 20 year old wiring is generally still very good but anyone doing the electrical test should have recommended an earth leakage circuit breaker .It might have one in the board. Most Landlords would be fitting a new consumer unit during the test when a new tenant comes in.
If they do fit another Mira sport, they are great units for steady temperature and flow. Used to fit many in University buildings.