It is not quite clear to me as to whether an isomon 3 is needed. I think that if blockmons are used then isomon3 is essential. Is this so?
With WatchMon CORE we updated the connection to the battery to a Hi speed CMU so that we could be more flexible with CellMate K9 and other future planned options. To allow the WatchMon CORE to still talk to the legacy LongMons and BlockMons it is essential to use an IsoMon3 as it contains extra isolation and other components to permit the LongMons or BlockMons to communicate with WatchMon CORE.
Hope this explains things more clearly.