What about Odyssey's claim that most chargers will not work because their charging voltage during the float stage is too low?
I don't know about their claim that most chargers won't work in the float stage, but their battery manual has a requirement of 13.5 to 13.8V "trickle" for winter storeage (when there is extended non-use) and/or parasitic loads present.
My BT+ shows 13.38 - 13.36V float 12 hrs after it clicks into the float stage, on 2 different installed AGM 28 AH batteries in my 40*F garage. This 13.5-13.8V Oddyssey "trickle" requirement is very close to Deka's AGM float requirement range (13.4V optimum,13.7V max.) in 70-80*F temps, so Oddyssey's requirement (trickle/float level) seems normal for AGMs. It seems that my BT+'s charge & float levels aren't "ideal" according to the battery mfgr. requirements.
I have noted that 12 hrs. after pulling the BT+ from the bikes, the 4.25 y.o. Westco read 13.03V, and the 1.75 y.o. Deka read 12.87V, so the little charger/maintainer seems to be doing it's job.