I am using the Cooler Master U3 as a pad, but mostly just as inactive holder for a better airflow. It has 3 fans, but they do little to cooling down, I guess they can help to reduce temps by 2 - 3 degrees.
When I really need to cool down, I use two "vacuum" coolers (lot of people call it vacuum, but it just helps to drain the heat a bit faster with increased airflow) from Coolcold.
I didn´t expect it to help much, but to my surprise, it managed to decrease the temp by almost 10°C! You can get them from Aliexpress, It´s super cheap while actually effective.
Here´s a video comparison of my A17 (2014) temps while running the Unigine Valley at high settings captured with NZXT CAM (don´t mind the GPU load, it only shows 0 or 99 load) with and without those coolers on both vents.