did they say anything about a reduced amount of airflow due to the 90?
Very little to no reduced airflow. It's only 90 degrees on the outside. Inside, there are 3 curved pieces of metal to direct the air around the corner in a curved fashion. You can see the heads of the screw that hold this contraption in place in the bottom picture.
There are some minor leaks in the connections. I'm going to get a tube of silicon and seal these joints up good, as my next step.