I have retired my Quattros from service and have reverted to the Merrills (and other cameras)
The Quattros suffer from what is, for me, four fatal flaws.
First, they clip the highlights far too easily. Unlike the Merrills, there is very little headroom and the highlights cannot be recovered in SPP.
Second, there is the issue with false colour infill between backlit high contrast objects like tree branches. This is linked to the first issue, because it only seems to be visible when the background is blown out, such as with distant tree branches against a blow out sky. This is wholly unacceptable in a modern camera. The last camera I owned that suffered a similar problem was a Kodak 14n - more than 12 years ago.
Third, purple blodges on grey / green areas, particularly in low light conditions, and even at low ISO. The Merrills may not be great in these conditions, but the Quattros appear to be worse. In fact, they are quite hopeless.
Fourth, while I quite like the camera shape for handheld shooting, it is hopeless for stitched panoramas using my Fanotec setup, whereas the Merrills are a perfect fit. A minor point, perhaps, but the DP2M and DP3M are near perfect for stitched panoramas.
In their favour the DP1 and DP2 Quattros do have better colour and slighty higher resolution, but that is not enough to make up for the faults.
Now I hope improvements may come with a firmware or software update, but I'm not holding my breath. At the moment, these cameras look like a dead end. The sensor needs a complete rethink. My preference would be for Sigma / Foveon to revert to the traditional Foveon X3 sensor, but I doubt that will happen.
Of course in appropriate conditions, great results are possible, but the operating window is so narrow it is very limiting.
It is all very unfortunate.