Do you mean the ones with the motor in the hand piece and they run off a car battery? WE used ours for the first two years, but I found them heavy to use (because of motor in hand piece) and my hand went numb very quickly (I have carpal tunnel syndrome in both hands). Also so much easier to nip them... I now prefer to hand-dag if necessary, usually just after lambing (that way I do a couple every day) and I halter-tie them to a corner in the pen.
Also as there is at least one (usually a Shetland wether) that won't be caught when the shearer comes... I hand clip them later. again tied up to a corner of two hurdles with the sheep held in place with my legs/knees. Not pretty but it works.
I really think that with such small numbers of sheep the cost is quite considerable... but if you want one, we really should sell ours....