i bought the blue-dot bobbin case for my janome MC6600 and it made a big difference.
once i upgraded to the MC8900, using the special bobbin case made no difference at all. (of course, i must point out that my FMQ on the 8900 is much more successful in all respects, so the special bobbin case seems to have been unnecessary.)
so i included the blue-dot case in the selling price when i sent my 6600 to a new home.
