The interface is very good and the thought that went into it deserves a good look. The only problem is the lightness is not maintained so you have to do a lot of experimentation to get it right.
In the end Photoshop is much more consistent and easier in an ICC workflow.
The problem in Photoshop/colorize is the printer is going to replace your color in the deepest of shadows hence your intentions are nipped at the bud. They too are using GCR in the sepia adjust in the driver however the B&W info goes through a better LUT based grayscale printing than ICC provides.
In this case the ideal would be a good rip like ImagePrint as neither the driver , nor Photoshop are perfected targeted for colorizing and printing through the driver.