I have the new bellman box... and think it is bang on.... its used 3-4 times aweek with the new and old collars (but not the first collars they brought out as they are not accurate) but the guy from bellman explained this too me over the phone.... spares for the old collars you can still get, apart from the casing.. as the company who cast them went bust... and i was told they are looking for someone else to cast them...
the box itself is quite large... but only as big as the old knocker boxes..its a sealed unit..waterproof... and you dont get grit sand and stuff stuck in the on switch lik