Flats = darker tone with thumpier attack. More fundamental and less overtones. You also get a lot less finger noise and fret clatter. In that sense flats are almost...stealthy. Perfect for recording.
Be forewarned that you might not flats at first. Without that zingy top end they can sound kind of dead. But as has been said a thousand times before (see the "Confessions of a Flatwound Convert" thread in the strings section), they really work in a mix. And once you get how they work in a mix, you can enjoy them on their own, imagining how they will sound in a mix. I have a P with flats (the CV) and a J with rounds (a Road Worn, which is a great bass) sitting right next to each other, and 7 out of 10 times I reach for the P.
When I tried my first set of flats, I switched back a week later. But once you get them, it clicks in. They're a little bit of an acquired taste.
My thinking on the fret wear issue is that flats versus rounds doesn't make much difference. I think it's more important with fretless, where the string presses directly against the wood.
RE the video -- the difference in flats vs wounds is so pronounced that it should come through even when the more subtle effects of fingerboard wood and even pickups are factored in.