Well, I made measurements between Advanced B&W (ABW) mode prints and neutral B&W prints using icc profiles on both an R2400 and 479/800 printers. The Advanced B&W mode prints are dead neutral between black and white while the "through the icc" prints had a slight hue drift from black to white. Not NEARLY as much as the previous version of UltraChrome and 2200/4000.79/600 printers. I guess it depends on what your expectations are. I'm interested in dead neutral-just like silver gelatin prints...
As far as the tinting, just like ImagePrint proved by eliminating yellow in their B&W mode, Advanced B&W mode uses effectively no yellow ink unless you drive the color tint WAY to the yellow/warm, which I would never do. With the numbers of +6, -3 or +3, -3 there is no yellow ink used. The blacks are warm enough to cover the slight warmth of slight tints.
The other thing I would point out is that from a workflow point of view, if I can use a single RGB archive file for both color and B&W (using the abilities of the Advanced B&W mode to convert to B&W) then it cuts down the proliferation of image file iterations I need to keep track of. Using the ABW mode proofing profiles Bruce and I have created, I can use adjustment layers to tweak the panchromatic results of the ABW mode of the driver.
The 3 black inks of the UltraChrome K3 inks and the ABW mode of the driver is a huge leap if you want optimal B&W digital prints. You can do whatever you want...for my use, the Advanced B&W mode has allowed me to finally produce digital B&W that meets or exceeds silver prints in every respect except for the limitations of the current gloss papers failing to match fiber based darkroom paper. But I have hopes of that changing in the future...