I've used a pair of these since November and they've performed pretty well. They are reliable and loud enough to alert the angler when his back is turned in the close confines of a boat. However in my opinion they are not really suitable for someone who is fast asleep, in fact they should never be used as an excuse for an angler to 'switch off' and not be vigilant whilst fishing. They would also be useful for an angler travelling light and roving when bank fishing though I haven't used them in this situation myself.
Lets be honest, it's very difficult for an angler fishing multiple rods from a boat to be looking at all the floats all the time, so at £5 each and they are definitely worth buying.
Where the boat biter could be described as simple, cheap & cheerful, Billy's Back Biters made by Steve Bown (aka Billy Two fish) are at the other end of the scale. I've used a pair throughout the last season whilst fishing from the bank for night time Zander in the summer and Pike through the worst autumn and winter weather.
The BBB alarms are a high quality piece of kit operating on the tried and tested rear mounted drop off style in the tradition of the ET backbiter. There have been many examples of this type of bite indicator around over the years but what sets Steve's alarms apart is the quality and attention to detail. These are not mass produced in the far east, they are made with pride and care by a genuine angler who only sells what he is happy to use himself. What really impressed me was the smooth indication of 'drop back' takes. When the fish runs towards the bank, the arm registers immediately and smoothly.
Steve makes these alarms in a variety of styles, features and colours including a very fetching Ipswich Town blue. Check out his website (link on the right hand side) where there is loads of information and you'll be sure to find a model to suit. The standard model retails at £40 and to put it simply, it's the finest bite alarm of this type available. These are highly recommended!