I used Tiles until they stopped working after a couple of years. They worked OK, but I had little use for them. I don't recall ever misplacing anything that had a Tile attached to it, so I wasn't motivated to replace them.
For your car key example, I'm not sure Tile would have helped. I don't think they are super accurate so although they would probably indicate that the keys were inside the car, I don't think they'd be able to pinpoint them to a specific location under a car seat. My experience with them was when they first came out, so who knows if they've improved their precision since then.
Regarding distant Tiles, when a unknown Tile is detected by the Tile app, it "phones home" and notifies the Tile servers where your Tile is located. This is a great feature, but it only works if there are other people in your neighborhood also using the Tile app.
Apple has a new tracking tile coming out "any day now" (lol) and I'll probably try them. The big advantage they are said to have over the Tile tags is that they can track items to within 5-10cm.