I have no idea about the new kit, but the original (expensive) DRL kit that I fitted does have a (grey) wire that I tapped into the sidelight power wire at the bulb in the headlight, which causes the DRL to dim when the sidelight / headlights are turned on.
I would suspect the new kit has the same functionality and I’d contained in the ballast box for each unit
Did you need to modify the bumper at all? The Mk3.75 version requires two extra mounting holes drilling per unit and some “trimming” of the bumper for a snug fit, so presumably you can’t go back to stock later. I don’t think your average auto-electrician will do the body mods (the sellers can’t fit them at their own workshop, either, because they don’t touch electrics) and frankly for over £400 you’d think they’d be the right size and a straight swap.