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 Prem., '13 TeslaMS85, three 156v CorbinSparrowsLi(NMC), 24v EcoScoot(LiFePO4)
EV Conversions: 156v '86 Ram PU, 144v '65 Saab96, 48v1kW bike
RIP(2021) ICE: Orig.Owner '67 Saab96V4, '88 IsuzuTrooper; '76 MBZ L206D RHD RV