It doesn’t restrict the vents to cover them with an air conditioner filter. The idea is to keep airflow, move radiant heat away from the CPU, and keep dust out of stuff. I made tabs of tape so that I could cover/uncover any ports, jacks, etc. The plastic keyboard protector with the elastic straps was a dealbreaker; it trapped heat and had to go. It all took a couple of hours at most.
I didn’t heat test beyond actually gigging in the heat. 
It survived marathon gigs at Burning Man in desert alkaline dust in 100+ heat. The only time I had a problem was a late-afternoon gig in direct sunlight on a 110-degree day. The CPU began stuttering. A friend literally held a fan onto the laptop and the problem went away.