This from the Sadowsky fb page:
Just received this report from Dublin, where U2 is in the studio...
Just a heads up on how wonderful your 4 basses are....beautiful instruments and so much "weight" and deep tone with a very light weight bass......amazing. The Will Lee is killer and the PJs so balanced. Adam has been tracking away and not having to break the momentum dialing in his sound.....Just a very good marriage of effortless tone that seems inherent with the overall design. The entire band and the production team could not be happier.
Nice one,
Dallas Schoo/U2
Here's one of the bass guitars. Looks to be a Will Lee model. Seems to be a custom finish job as well.

I've a message into Sadowsky as to see about getting a bit more info on the 4 bass guitars.
it makes very difficult to play in time, and it doesn't extend the sustain enough to make it sound like an ebow, so it's pretty much useless in my humble opinion. Anyway: let the forum's big fishes speak
And it would be an addition to a big order I'm gonna make, so shipping isn't to worry about.