I used those same things, except they were 3/4" F NPT on both ends. I will say this.... they are not as flexible as I thought. My copper pipes were already in place on the wall, and I had to do some de-soldering and re-soldering to make it work. Those stainless connectors provide some stand-off from the wall, and a little bit of radial flexibility at the softener, but not much. Since you are going from PEX to them, you will probably have more than I did, and be just fine.
On another note, you will probably want to tap into the city water (pre-softener) for things like outside hose bibs, refrigerator/icemaker (or some other drinking water source, unless your current water tastes bad). I was fortunate that my house was already plumbed that way.