I find that the last two (?) double shots from the MXK's hopper are much inferior to the earlier shots. As I use a bottomless portafilter it is very obvious.
Dr.Chris - I seem to remember that owners said that the Mazzer's doser was not a strong point and needed tape on the flaps to sweep cleanly so I wouldn't suggest finding one for your grinder.
However, with a Rocky doserless I kept having little clumps of ground coffee fall out of the chute after I thought I had cleaned it meticulously (messily annoying). I also think the distribution of the ground coffee is better from the MXK's doser than the Rocky or MM-E doserless. So, some dosers are helpful - I asked for a doserless MXK originally and couldn't get one but I wouldn't swap mine for a doserless MXK now.
Cheers,
Hugh