The install is actually pretty straight forward. The sides with the seatbelt clips obviously just clip into the existing seat belt holders.
The side with the eyelets basically bolt into anchor positions in the car. They attach permanently. But you'll notice that they do have seat belt clips and receptacles, so when they're not being used, you just unclip them and you're good. The portion of the strap with the eyelet stays in the car, but it's a pretty small strap.