Digital BW, The Print

According to the MIS website, you can replace the Piezotone ink 
with MIS FS. (appended below.) The price differential is very 
compelling. 
--Can I just pour in MIS FS on top of the 1/2" of piezotone ink 
remaining in the CIS bottle? 
--Have others done this? 
--Are there reasons NOT to do this?
John

http://www.inksupply.com/index1.cfm?source=html/workflow_ne
w.html
<<FS and FS Neutral for Cone's R9 Driver (Image Export BW by 
R9)-The MIS FS inks will work with Cone's R9 driver. No special 
workflow is required when used with this driver. It is a lower cost 
apporach and the print results	are reportedly equal or better. 
These FS inks are fully pigmented, with pure carbon pigment 
and they are archival. The performace in cartridges and in 
contiuous flow systems is identical. These inks do not cause 
clogging problems, and they do not evaporate when the printer is 
not being used. They are compatible with the Cone inks and can 
be substituted one for one with out cleaning or flushing. >>