I've been using the pistol grip filter for about 2 years.  It screws in between the brush and the airline.  I have 2 Iwatas, an eclipse bcs and a revolution br.  I leave the filter on the airline and just swap the brushes on and off.

It's great in the revolution as it's a gravity feed.  It's a bit rougher to use on the bcs because it's a bottom feed and there's not a lot of room between the filter and the bottle.  You can only use the narrow Iwata 2oz and 4oz bottles, nothing else will fit.

-Fred