When power sweeping the brush head through centrifugal force expands to suite the flue you are sweeping it also centres itself, therefore you do not require a vast range of brushes. Because it is not a traditional brush there is no surface tension being created in the sweeping process as the head adjusts to fit the flue. You adjust the force of the sweeping action by increasing the speed of the drill this has the effect of stiffening the brushing action. So if you are doing an older style chimney then you would use a low speed however if you are doing a heavily built up clay / steel flue then you can up the speed giving you an unbelievable cleaning action. Also the action of sweeping clockwise positions the head to the right hand side when sweeping a larger type chimney likewise reverse the drill and you then sweep the left side. In short you clean chimneys more effectively causing less strain on the structure of the flue and making lighter work for yourself.
It is good to remember that this is a new method of sweeping and as anything new one has to adapt to it. When rotating anything you build up heat, think of drilling if you come to a point where the drill gets stuck you can see the end of the drill bit glow. Likewise if power sweeping and you hold the rods in one position you can cause the friction heat to build up rapidly and this can create enough heat to melt the rods. When sweeping up the chimney if you come to a point where the head is not moving stop pushing up bring the rods down a bit change the direction of the head from clockwise to anti clockwise and try again this should allow the head to re position within the flue. Caution should also be used for the same reasons when removing nests. As this will be a new method to you and when you first use it you lose the same feeling that you used to have down the rods but in time this returns. There are two sizes of head for power sweeping and they are strung differently. The smaller head is designed for sweeping flues attached to appliances, woodburners multi fuel stoves etc. The larger head is for all other flues in other words the head size is not a factor in power sweeping as the head adjusts to fit the flue it is sweeping.. When using any power tools caution should always be used.