I use them, amongst other ways (leaflets and YP etc.). I find they work very well for the outlay. I advertise in about 5. They cost between £ 80 and £ 200.
But they have to be in addition to other sources. The responce is not enough to rely on. I have one which costs £80 and so far this year has provided £ 1200 of business. Not a bad return, but not enough to retire on. Also its nice to support local Churches/Charities.