I got excited about slot car until I saw the words around them.
We have these in both cars. In my wife’s car i turned the mount upside down so it didn’t interfere with the nav. Much better than vent/magnet mounts.
Will this work on the 8 track player in my car?
These are generally a very good use for the slot provided you do not over tighten. If you do, you run the risk of having plastic chips disable your CD player. The player may still function (my seldom used CD player still does) if the pry arms are shallow and do not touch the CD.
An added benefit is that this mid-dash position generally avoids sunglare on the screen of your phone and minimizes obstruction of the road.
Some such designs might hold at widest expansion. If feasible it may be better to save up and replace everything around the 8-track player except the driver.
Consider your car is older than my 13-year-old vehicle… We have arguably gotten value out of our purchases and need to be a bit careful. A co-worker’s axle broke while driving. That was not fun.