If target presentation is close and open, such as rabbit targets, it can't be beat. I also use it on other close targets. On most of the close shot sporting clays ranges that I shoot on, I use the defusion/IC choke combo a lot. Mine patterns very good in my 28" barreled 682. Bill
I have not used the diffusion choke, but have Ballistic Specialties Cobra chokes for all my guns. They work extremely well. Most Sporting courses can be shot with this choke alone. It breaks targets out to 45 yards no problem.
8 1/2's pattern best the best for me, but all sizes work.
I actually stopped using my Briley diffuser chokes because the more I thought about it the more I figured it was blowing out my pattern. I'm probably wrong but my thinking is this - it's putting a twist on the wad and thus spinning the shot that's in that wad. I'm figuring that once the shot exits the barrel it's going to head in the last direction it got spun in. Like I said, I am probably wrong. Mine where in my 682 12 ga. I did some patterning and it was pretty inconclusive, but I'm still not going back to them.
PS - the good thing was that I didn't buy them, they just came with the gun.
FWIW, I have patterned several dif 'diffuser' and rifled chokes in several dif guns, inclusive of Briley's in Berettas and 1100's, Remington 'rifled', a couple of other makers rifled chokes, one was a deer/sabot type choke, another a 'special' [read that anyway you wish] rifled choke. I have also played with Raye bored bbls. My experience is that when using plastic wads, in other words conventional quality target ammunition, they [difusser chokes] shoot IC pattern percentages.
If you are using a plastic wad w/no petals or card wads then you may get more open patterns .. or you may not. There is no way to really tell unless you pattern the specific gun/load combination.
If you really want open patterns, it may be better to either buy commercial 'spreader' loads or load your own using something like a post wad for choked bbls. or purposely deformed shot. Higher velocities can sometimes open patterns as well.
Its interesting that reclaimed shot often shoots sufficiently good pattern percentages for some people to use it w/good success for their bunker shooting. A lot of reclaimed shot is not all that deformed, it was hard shot to begin with and mostly stayed that way when fired.