Not that it really matters in this particular instance since the command ends right after the variable is set, but a here string can be used here instead of the echo + pipe. In my opinion it looks cleaner and if the script did go further, it could run into some issues using echo.

double quote to prevent globbing/word-splitting

Great catch! I just put up D4453 addressing it since it is the final single-bracket usage in a shell script in the codebase.