Ian;
Power Brush wands (revolving brush spindle) is a great way of cleaning low nap commercial carpeting in that is provides the (sometimes) necessary agitation to break down surface tension.
As I believe, John Bolton referred to, they tend to be alittle more bulkier perhaps in tight areas where a traditional wand would be much more preferable.
However, sometimes it is a must to have "mechanical action" at ones desposal to complete the job in great fashion. And, this is where the Power Brush might come in handy.
As far as its "Popularity", in MHO, it unfortunately is not very popular (at least here in the US) and we, for example, have discontinued this great item only for this reason.
Don't know if any of the above information I offered helped; however, I wanted to post my opinion.
Good Fortune to small business;
Ed Valentine
cross-american corp.