We have been using bb talkin now for a couple of months now and it works great if you know the downsides of bluetooth. So the range isn't unlimited but with a master/main combination i kept contact up to 6/700 meters, i didn't go any further. A main/main combi indeed might have a range of 1500m. Question is do you really want your students at 1500m away from you?
So as an instructor you should wear your unit on ur head also, or stay on the beach so you are on a higher location than your students. This is important when teaching bodydragging, as soon as they are getting on the board there are hardly any disconnections.
If you loose contact, dus restart the unit(s) and they will reconnect, so no pairing up process again in the water.
Every instructor here is gonna get his own set next year and the students are really making more progress and wouldn't want any lessons without them. I found that a lot of dads/mothers also have an eye on the system for there younger children, they can keep in contact with their kids on the water while they are on the shore or on the water also.
Got ours at www.bb-talkin.eu