I hear both good and bad about not only the Hayden, but just about everybody including the Derale pwm units. I think I’m going to build my own control system, there’s not much to it. The plan is to replace my thermostat housing with one that has a 1/2” npt bung, purchase a metric M14x1.5 to 1/2” npt adapter bushing, buy a BMW dual stage temp switch from Rock Auto and use (3) 40 amp relays to get a high and low speed. I’ll series my two fans for low speed and parallel them for high speed. Doing this should not only give me good control, but should eliminate current spikes. Also if either fan or relay should fail, at least one fan will still work on high.