Andrew, to answer your question, my wife and I had used two of these mechanical timers for about 5-7 years on our two i-MiEVs with no OBC issues (touch wood). Since I almost always never charge to 100% and want to stop the charging at around 12-13 bars, it became second nature to simply eyeball the charge level and crank in the time. I stopped using these timers out of concern for the OBC and now use the clunky Remote, which takes a bit more time than simply rotating a knob. I'll replace the fuse when the OBC warranty expires. I'll now go back to using at least one of these timers as my wife never got the hang of using the Remote and I sometimes find myself in the doghouse for not having charged 'her' car.
EVs: Two '12 Wht/Blu SE Premium, '13 Tesla MS85, '20 Hyundai Kona Ultimate, three 156v Li(NMC) Corbin Sparrows, 24v LiFePO4) EcoScoot EV Conv.: 156v '86 Ram PU, 48v1kW bike wheel Mothballed ICE: '88 Isuzu Trooper RIP: '67 Saab 96V4 owned 54 years