I struggle to find availability sometimes, but I recently subscribed to KVS on the advice of others on FT and have never looked back.
There was availability around when I wanted it and to the right places, but the online BA system being such a chore to use made it very much a hit and miss affair or at best a lengthy process.
With KVS, stepping through each day +/- is an absolute doddle and being able to reload previously saved itins to check for updated award space makes it really quick and easy.
I was able to find 4 x F awards for MAN-LHR-JFK-LHR-MAN for December in about 10 minutes. Then go to BA and using the exact criteria book the flights I wanted.