The Isobar 2092 control valve is a modified version of the Fleck 5600.
That makes it very proprietary to Amtrol/WaterSoft dealers or plumbers, and there are very few WaterSoft dealers. And if I'm reading their specs right, it is a 1" ported valve, unlike the 5600 which is 3/4" so I doubt many stock parts will be able to be used to repair it.
The CS version of the Clack WS-1 is a much better choice. And Clack is industry standard stock stuff, not proprietary to one company so there are many dealers to get parts from.