anybody use them? How well did they work for you?

I was curious about the Hastings Paradox "sabot discarding" chokes a couple of years ago... it's a 5" extended rifled choke that is supposed to "discard," or I suppose separate the sabot at the muzzle.

Although I don't have any experience, I don't think that a sabot slug grabbing 5" of rifling after twenty-some inches would make much of a difference at all (that and the fact that the choke itself is $58 and the cheapest sabot slugs are more expensive than the most expensive rifled slugs (ok for the most part)).

I have one in a Mossberg ATS535, I did not notice any real improvement, but it does foul quickly.

The concept of having the last inches of the barrel rifled is as old as the hills. It was the basic concept of the Paradox Guns used in Africa and India.
The concept was to put a slow spin on the large solids in use at that time. Those solids were more or less "squared", menaing the length equaled the diameter........thereby needing very litle spin to stabilize it. The twist in the original guns ran about one turn in 80". Since the original solids were hardened and the twist was slow.....they did not skid when the velocity was around 1200'/".
Now......Today's rifled choke tubes has the same fast twist as the rifled barrels. When a soft swaged lead slug or sabot hits it at a higher velocity.....they do skid and foul.
We tested them with our hard alloy heat treated solids.....and the loads torgued the choke so tight we could not remove it!
So......the concept is correct if it had a slow twist, but then it still would not stabilize the longer bullets used in today's sabot rounds. These rifled choke tubes of today are a compromise at best.
With that in mind.....the hunter would be better served with a smoothbore and slugs designed for it.....or a fully rifled barrel.
All in All, the rifled tubes are an iffy affair.
Regards, James