The ideal plug for any FP's is in fact the OS #6 (formerly A3).
The Idle bar glow plug is from the dim past when virtually all model engines used some form of loop scavenging. The piston top dam tended to shoot fresh charge directly into the plug coils, tending to dampen the ignition resulting in poor idle and or throttle response.
Most all modern engines use a number of porting senario's with no piston top dams. Therefore the idle bar plug is somewhat redundant.
John