Here's a link to a review of the Smartjet:
http://www.cybermodeler.com/hobby/tools/iwa/tool_iwa_smartjet.shtml
It appears (but I'm not positive) that the Smartjet comes with adaptors so other airbrushes, such as Paasche, can be used with it. 'Quiet' can be quite subjective, but I've never heard any complaints that the Smartjet is too loud. It can't be any louder than my Paasche 500!
I'm looking into getting either it or the Sprintjet. I've heard from a couple of sources that the automatic shut-off on the Smartjet doesn't operate at the lower PSI that modelers typically use, so it's an extra feature you would be paying for but not using, unless you use the airbrush for other applications such as t-shirts. I've also heard that the 'regulator' that comes standard with either model is only a bleed-valve, so it can be difficult to adjust to a specific PSI. As a result, I'm leaning towards getting the Sprintjet with a true regulator. It looks to be cheaper than the Smartjet but will do the same for my needs.
You might want to do a search in this forum and on other modeling websites, like I've done, for past posts on Iwata compressors.
Hope this helps,
Mark