I am presuming that you are shooting walked up stuff then ? If you are shooting driven game, who the hell is going to see your chokes ? Carry your gun to your peg in a slip, remove from slip, use, replace in said slip ! I could not tell you what sort of gun either of my neighbours are using at any driven shoot that I have been at, BUT I could sure as hell tell you HOW they removed it from it's slip AND on 1 occasion how clean his barrels were (I found myself looking down them a couple of times) as to what sort of chokes...well ? Save your money and shoot yer socks off ! If you shoot well, you may find they ALL have extended chokes on your next visit.
If you feel that flushing them could do the trick, then do so, but to buy flush chokes could just be money down the drain !
I occasionally use my S x S for shooting clays, it is an 80 year old English game gun. I rarely find that clay shooters object though !