The filler can be used with the Water Miser simply by adding a piece of clear plastic tubing to the end of the filler nozzle to compensate for the height of the Water Miser. Or, the Water Miser's can simply be removed to water the battery as you would with factory installed vent caps.
The Plews filler is a one stop shop that adds water to the same level on all batteries. Typically, different manufacturers recommend different amounts of water. It is best to read the maintenance manual usually available on the manufacturer's website. The Plews filler tends to overwater most batteries causing excessive electrolyte buildup on the batteries.
Hope that helps.