re: Why use SDKMAN and jenv? The whole idea of both is to simplify management, and SDKMAN's functionality is (mostly?) a superset of jenv's, so... why ...
 

Maybe one exists, but I haven't yet found a way to quickly and easily switch between Java versions with SDKMAN. With jenv, it's as easy as:

$ java -version
openjdk version "11.0.2" 2019-01-15
OpenJDK Runtime Environment 18.9 (build 11.0.2+9)
OpenJDK 64-Bit Server VM 18.9 (build 11.0.2+9, mixed mode)

$ jenv global 1.8

$ java -version
java version "1.8.0_201"
Java(TM) SE Runtime Environment (build 1.8.0_201-b09)
Java HotSpot(TM) 64-Bit Server VM (build 25.201-b09, mixed mode)
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