I've not used the Web seal stuff, but am aware of it. After application, it needs a UV sealer applied over top of it. Notice the texture of the top surface.
Compare it to
this which has the smooth surface on top, which is the UV protected material already applied.
IIRC, we called Eternabond way back and that's why we with with the white UV protected stuff.
I don't know where you'd use the Webbed stuff instead...maybe over a larger area or somewhere you'd want to see a very uniform surface? It might take some of the rubber roof coating stuff nicely? But I'm guessing at those uses.