Tim, I think the Rex engine unreliability is a bit of an urban myth, if the user has been really good at charging and run for weeks on pure EV then the car automatically runs the Rex engine through a cycle ever so often, you get a dash data warning and then it cuts in mid journey

You can also force the Rex to run if the battery is under 70% charge, (which I did before a long journey with no charge points) so you can easily test it

Jon M