The DC25 is a much better machine and it actually has a ball, instead of two large bowls on the side forming a "V" ball, it's just not good
DC25 is much more durable, has two rows of stiff, fat bristles which stick out to give a good beating (for a Dyson anyways) and it is much easier to clean out a clog, the pipes on the side are removable and can be washed if you find they get dirty, with the DC40, the pipe and all the stuff is inside, you will need a screw driver to undo a screw and remove the hose pipe in the ball.
DC25 has a metal wand, instead of a plastic bendy one like the DC40.
I tried a Dc41 for a week in my home, and turning the ball made the top half of the vacuum twist, especially the handle which turned due to the flexible plastic. I would say the DC25 is a much better buy, or you can use your DC33
To take the brushbar out with the DC25, you need 1 coin, and the brushbar comes out the side, like a Sebo X1/X4. The DC40/DC41 needs 4 screws to be undone in order to remove the brushes.