I think that inertia starters have a poor record with the Rover 4 cyl engine. Probably this is because a lot of times the engine tries to start, but not successfully, so it gives the pinion a hard time. I had an inertia pinion crack from such abuse. The pre-engaged starter solved this problem, but after a good few years also this gave up the ghost, so i went back to an inertia starter that i have kept as a spare. However now i am using iridium spark plugs, and engine always starts cleanly even after staying inactive for weeks, so the starter doesn't suffer.