The FX1 lens is attached to the cam, but you're still able to use an additional wide-angle lens. Not completely different lenses though.
If you want decent audio I'd go with the Z1U as you can attach pro-mics and don't have to use something like a Beachbox to get XLR inputs. Furthermore you aren't stuck with Sonys consumer-support but get to talk to their broadcast division.
So, depends on what you want to do with the cam, but if you're going to do serious work and can get a good deal on a Z1U, I'd say to go for it instead of the FX1.
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