It is interesting that you mention the difference between other filters and the C150. For interests sake I tested the water in and out of my current filter which is a 3 stage sub micron filter which includes a softening stage, and is not a whole lot cheaper than the C150.
The results showed no change to GH or TDS. I suspect that if I tested immediately after a new cartridge is fitted I would see some improvement but obviously it can only soften a small volume of water.
I think this really highlights what many sponsors have already stated, that a high quality drinking filter is not necessarily suitable for espresso machine use.