I just got my Omni 4000 in the mail so I'm on week one. First impressions are not good. The Iwata is much more solidly built. The color cup on the Omni looks to be a bear to clean. Pic links below. The iwata cup is polished on the inside and is tapered to match the milling cut from the body of the brush. Breeze to clean. Also the Omni looks nearly identical to my Badger 100LG with the exception that the omni has an open handle for access to the needle. The color cup on the 100LG is designed with a smoother attatchment point, so I'd bet that the 100LG would be easier to clean than the omni. One could say (in a very general way) that the design relation of the 100LG to the Omni is like the Revolution CR to the Eclipse HP-CS.
Here's a pic of the Iwata color cup. Very smooth joint
http://www.plummersmines.com/modelling/iwata_cup.jpg
compared to the Omni. It seems to have been attatched sloppily. Note the rough, uneven attatchment point.
http://www.plummersmines.com/modelling/omni_cup.jpg
Even the sotar cup is smoother (the 100LG is also but I lent it to a friend so I couldn't take pics.
http://www.plummersmines.com/modelling/sotar_cup.jpg
It's hard to tell from the pics but on close inspection the trigger mechanisms and main body structure on the sotar and omni (as well as the 100LG) are identical.
http://www.plummersmines.com/modelling/omni_sotar.jpg
Proof is in the pudding, or spraying and actual cleaning. first try tomorrow.