You can learn from each test.
Scenario: I was just asked about two slabs this week. Both are in the mid to upper 90's rH.
One slab had an MVER of around 3lbs. The surface was burnt black and had a curing compound applied immediately after the pour. The slab was in an enclosed building, so I question if the self-dissipating curing agent ever dissipated. Most of these need some UV light to break down.
The other slab was porous and had an MVER of almost 10lbs.
Here's where the thinking went awry... The person with the 3lb slab thought his slab was dry enough, or very nearly dry enough, while the person with the 10lb slab thought theirs would never dry. Remember both were over 93% rH.
The company with the 3lb slab was willing to continue waiting for the rH to drop, and the company with the 10lb slab was ready to throw in the towel immediately!
I explained to mr. 10lb slab that his high MVER was showing the slab was drying at a rapid rate, over a gallon of water per day per 1000sf in fact. If he can promote drying like that, he may drop the rH quickly. But the 3lb slab is holding water and will take nearly forever to dry. (Forever in flooring speak is > 2 weeks
Another kicker in this story was the CaCl tests were done improperly and the surfaces weren't prepped right. In this case though, when you are measuring the actual concrete surface that you will be gluing to, I think you gain some important knowledge.
CaCl tests can also indicate a recent wetting or flooding of a concrete floor which the rH test will not pick up.