I fired up the DRLs to test them before installation:
(click to enlarge)
They're bright - very bright; I can't imagine the OEM DRLs would be any brighter! And yes, when you power the blue wire (i.e. when you switch on your headlights) the DRLs dim.
And here's the wiring loom showing the 2 x relays
I've noticed some of the DRLs on ebay only appear to have one relay: I assume this means that they don't dim when the headlights switch on?