it's $1,200 or $1,300 to completely review and upgrade both units. Maybe it's gone up since I last checked?
It may not be an option now anyway, I think they were dropping support for their older units soon.
I've only read that a polarising filter was much benefit when measuring uneven glossy materials like gloss canvas.
Maybe one of the more knowledgeable folk here might like to comment on whether the latest kit like the Isis and i1Pro2 now make the Spectrolino redundant ?