Bagged vacuums are great for easy clean up, great filtration and most normal cleaning situations, I think they would be more widely accepted if you had a better way of monitoring how much is entering the bag.. because on most jobs, seeing where the soil is concetrated is a huge advantage.
(and the cheasy soil alerts on hoovers and kenmores just don't cut it in my book.)
To the question at hand, from my limited experience and reviews by peer cleaners, they seem to be very well built and great quality vacuums. Its another one of the vacuums that homeowners don't have access to easily and hence can set apart a great value in some customer's mind.