A good A/G is of great benefit. As a frequent visitor to Sleap I've found them very useful in the past and thankfully, I've never had the experience of a bad one. I've personally witnessed two potential accidents where pilots had not seen other aircraft on finals, cut into the circuit and been warned off by A/G. It's not nice to be just on very short finals and to look up to see another aircraft descending onto you from above and behind! Using a common air-air frequency is great providing other aircraft are 1) radio eqipped and 2) listening!