It's a pass for me. He's not better than what we already have.

Seems like there are two factions here -- one that wants to see some blue line upgrades and willing to pay, and another that wants to hold firm.

I think there are several defenseman out there that would improve the blue line, where the Blues have been undeniably weak this season. There are the more expensive/sexy options like Giordano and Chychrun, but also some less heralded guys like De Hann, Lyubushkin, Wideman, Pysyk, Mayfield, and Kulak that I think would provide an upgrade or at a minimum some depth. Even if you stick with Mikkola-Parayko and Faulk-Krug, Bortuzzo hasn't exactly set the world on fire this year and I'm not comfortable at all with the RD depth behind him should someone get hurt. There is a bit more depth on the left with Krug, Mikkola, Perunovich, and Scandella.

It would be a very Doug Armstrong move to add a depth defenseman at a minimum. Who plays if one of the RD get hurt?

My fear is that Chief will bench Perunovich come playoff time for someone with more matchup / PK ability, so I think the natural move would be to add another d-man and try him with Parayko to see how it looks. I also have doubts about whether or not Mikkola is going to hold up his end of the bargain for 19-20 min per night on the shutdown pairing for the rest of the year, although he has been pretty good most of the time.

I haven't put too much thought into the exact guy they should go for, but I think your list is fairly comprehensive. I worry about the acquisition cost of Gio or Chiarot so I think maybe going for more of a bargain option makes some sense (unless they're going to pony up for Chychrun). And I think you could get a stay-at-home RHD (say Mayfield) and try a few things out, one of them being Faulk-Parayko, Krug-Mayfield, Mikkola-Scandella. Not ideal on the handedness but I like the chemistry/TOI spread.