The Run In And Break is a joining manoeuvre, any aircraft joining should not break into the circuit until the pilot has all the other aircraft in the circuit in sight. He/she should know how many are in, as the controller normally tells him 'X aircraft ahead' at initials. This is what was the practice when I used to instruct the RIAB in military aircraft.
As the procedure is primarily designed for reducing energy prior to the downwind leg (with a secondary advantage of minimising your exposure to groundfire), it's pretty pointless in any aircraft doing less than 200 knts.
But my main point is that everyone in the circuit should know where initials is so they know where the threat is coming from if the RIAB procedure is to be used. If people don't know - then it doesn't really have a place at that airfield.