My girlfriend had a Dual HU in her 2000 Ford Focus, it stuck out about an inch or so due to the way it was made. It has a drop down front panel and protrudes a bit. You push a button and the front panel comes out and drops down so you can insert a CD. It was ok but it developed a problem where it would just cycle up and down all day. It was very annoying. We replaced it with a Pioneer HU.
It also depends on the dash kit you are getting. Some of the EL Cheapo ones will make it poke out. I don't like the look of them at all. The ones made by Metra are good and the Schoche brand is decent as well. I already had a Kenwood in mine when I bought it. So when I replaced it with the newer Kenwood unit it was just plug and play.
I'm not sure who made my dash kit but the texture and feel of the plastic matches the HVAC controls perfectly. I'm very happy with it.
1996 Blazer LS 4.3L 4x4
2001 Ford Taurus SE