On my Envirodri the rod holding the brushes in place just push out - I use a screwdriver to start them off them I can pull 'em out by hand.
Reverse for going in but can be a bit of a pain at times to locate the rod in the hole at the other end - if you find an easy way of doing it - please tell me!!
5 different brushes in total - black, black/white, white, gold/white, gold. Black is hardest and gold softest. About £85 pair +vat. Should last long time.