The RS2 sling is the slimmed down brother to the RS1 loop sling. They are similar except for the fact that the RS2 lacks the reinforcement to hold the loop open. This means that the RS2 is flatter in profile than the RS1 and is a bit slower to use.
I compared the speed of the two slings in a photo sequence. The camera takes roughly five photos per second, which offers a rough measure of the relative speed of each sling. I began from a standing position, unslung, with the rifle held at the ready in port arms. I slung up and assumed one of my favorite positions, the rice paddy prone. You can review the photo sequence with the RS1 sling here. The sequence took approximately 4 seconds.
The differences in using the slings is that the RS1 allows for, and almost demands, an explosive movement that begins right away. You just burst into the loop and take a position. The RS2 begins with the loop flat. That means you have to slow down to find it. Once the hand is in you can thrust the arm in explosively.
The second difference in using the RS2 becomes apparent when the loop reaches the upper arm. It is possible to get the loop to reach the proper spot on the support arm a majority of the time given practice with it, but this is also dependent on your clothing at the time. It’s also possible that after the arm is thrust in the loop will end up near the elbow or mid-bicep. In this case it will be necessary to reach over with the firing hand to pull the loop up once in position.
The following photo sequence shows the RS2 being donned while the shooter assumes rice paddy prone. It was done on the same day as the RS1 sequence, with the same clothing. This took approximately 6 seconds, which was 2 seconds slower than the RS1 sling doing the same thing.