There seems to be a very wide range of opinions concerning Miller. I found a good article to share that was evaluating which of their defensemen could step up when Nate Schmidt got suspended 20 games in Vegas. Miller is discussed in the middle and I think it is an excellent description of his good and bad attributes.
How the Golden Knights can replace Nate Schmidt on the top pairing
Miller is more well rounded than most of our 4-9 defensemen. He is a great third pairing right defensemen. He should not be relied on to be a top two pairing guy long term, but can step up into the role as needed without a huge drop off. He has all the tools to be top four except his average hockey sense. He is a little slow to diagnose and predict plays which leaves him prone against top offensive lines. For me, him and Risto are both solid third pair right defense. Both are signed for the next three years becoming UFA's in 2022. Miller costs $3,875,000 vs Risto at $5,400,000. Both are a touch expensive for a third pairing guy, but especially Risto who is getting second pairing money. Montour will be an RFA and will need a long term contract if we are keeping him to be the long term second top 4 RD with Joker.
If we intend to resign Montour, and are stuck with Bogo due to his contract, then I am trading both Risto AND Miller to free up cap space and fill 2C, 2LD, 3C, of 2RW depending on what opportunities are actually available to trade.
If I am only trading Miller OR Risto. I trade Risto because I think he brings me back a touch more in return, gives me a bigger cap relief, and is less versatile (which is a characteristic I want in my 3rd pair D.