I know, I know. It's not that yours don't work for you, but for one, they don't work as well as a good maintainer does.
More importantly, to me anything electrical from HF is scary, and I have several smoked angle grinders to back that statement up. I do have multimeters from HF, but they aren't connected to 110 V.
As you know, I'm a firm believer in desulfation, having used BatteryMINDer, PulseTech, and Canadus products for decades. So even if your HF units are working and haven't caught on fire yet, they are still lacking that important feature.
Come to think of it, maybe I should send you one of my BatteryMINDers so you'll have a better chance of your Kubota battery (and those are very good batteries) last as long as my oldest one has?