This thread at AK holds reviews from early adopters who have put them into RS1b and RSIIb speakers. So far it's unanimous - they are a big improvement over the stock, and can be added one pair at a time (i.e. the high mids in RS1bs) and still blend with the stock units. Clarity, detail and an ability to play louder without distortion seem to be the obvious advantages.
http://www.audiokarma.org/forums/showthread.php?t=301204
http://www.audiokarma.org/forums/showthread.php?t=301204