Unless the product specifically states it won't harm microbes, it likely does.
In my experience, most people don't actually need CalMag, they just have a lockout of some sort and CalMag almost always makes their issues worse. Excess potassium and calcium can lock out Mg, as can poor pH of course.
One can foliar feed with Epsom Salts for Mg until the pH/nutrient issues are corrected.
Langbeinite can be good stuff, but under two conditions: 1) You are 100% certain K isn't the cause of your lockout, and 2) It is used in small doses.
Ca, Mg, and K are very much intertwined with one another. If one is in excess, the others will be locked out. This is especially true with Calcium, as "
Most of us have enough or too much calcium in the soil for plants to use just as a nutrient. The more calcium in your soil, the higher the pH of your soil can become."
Here's some more information on the relationships between Ca, Mg, and K in the form of pdf files for anyone interested.
Effects of K, Ca, and Mg Ratios in Soil
K, Ca, Mg - How they relate to plant growth
and an article
on calcium from NOFA, which has loads of valuable information.