Correct Chris...they are great for "free" roving livebaits in shallow water. For some reason they dont tire a fish like a normal float does. With braid you can acttually steer the bait in the direction you want ti to go. The fact there are "two" floats allows you to see what way the bait is swiming.
They are best used from a boat, because you can just lower the bait over the side...and away it goes.
Marvic have been selling dumbells for years..and Harris have had them listed for about 5 years.