Safe to buy brass compression fitting/pipe transition?
From a corrosion consideration it should be good: Except check that the clamping screw on the CTS end is stainless steel , non-magnetic would be best.  A steel screw would not likely last long on a brass/bronze fitting underground. The fitting has a more reddish color than yellow brasses which is means better corrosion resistance ( less zinc and more copper and tin). This answer if for buried in the ground or a valve box.