Questions regarding the types of soil tests (Reams)

I'll elaborate later in the post, but I'm wanting to understand more about the types of soil testing and it's receptiveness to accuracy and such.

The two tests I've heard about is mehlich (1 or 3) and something called a "Reams" test. The mehlich test seems to be the standard test that most labs run. Today someone mentioned to me about a test called a reams test. This test seems to be more for what they said "biological" practices or at least more common? I don't know if I'm supposed to associate this with "eco friendly" or just a different term.

The reasons they gave that this test was better was that the Reams test will show you what nutrients are available to the plant. The other tests they said might show that there are loads of nutrients but the plant (grass) can't access it as the nutrients are locked away in other forms? I'm not sure of the validity of this.

For the turf management industry is the Reams test something that is generally accepted? Is the statement accurate that it's better because it shows what nutrients are available? Or is this something less proven?

How this got brought up was in my quest to find a supplier of Harrell's fertilizer, I called a local lawn/weed and maintenance company. I got put in touch with the owner and we had a good 45 min conversation about lawn care. Super nice guy. He mentioned that he doesn't use synthetics and has moved to something. sled biological fertilizers. He gave his reasonings on switching and then we started talking about specifics of lawn and got on the discussion about soil tests. We got off into the weeds of talking about all kinds of stuff, mostly "biological" cultural practices. He seemed extremely passionate about lawn care (i guess you would have to, to own your own turf management company).