I've used them. They are good at removing built up fouling, but if you clean regularly, you won't need a tornado brush. I can't think of a reason not to use one though if you already have one or it is all you can get.
I'm not sure how I feel about running a stainless brush down my barrel. I caught it on sale at cabelas in a three pack. Came with a copper brush, tornado brush and a mop, 4.95. Couldn't complain for that price, I just needed a new mop but when I saw the sale, I figured why not.
I have used them in the shotguns for years. The man above does bring up a valid point about the stainless steel brush may be hard enough to scratch a barrel. I inspect mine for broken wire tips EVERY time BEFORE I use it. If any of the loops are even kinked, I replace it. They last a long time, between the 12 and 20 gauge, I have only replaced 4 or 5 in the last 20 years. I really like to use them as a "springy" jag for pushing flannel patches through. They really keep the fabric pushed against the barrel. Since it is all loops and not points, the cloth does not het all embedded in the brush either.
I was looking at the brush at Cabelas when the guy behind the gun counter stated those brushes may scratch the barrel. So I bought the standard bristle brush.
For removing plastic fouling from smoothbore shotguns they are great... I used one a LOT when I was big into trap shooting...
I don't see any purpose for running one through a rifled barrel though. It won't get in the grooves very well and definitely will not get the nooks and crannies near the edges of the rifling lands. May also case premature wear on the edge of the lands.
I think they have their place... that place is in smoothbore guns...
I bought one of these Tornado Brushes many years ago simple because it looked cool. It is still unused. I use a bore snake or the regular copper brushes in my barrels. I still have the Tornado. I may just drill a hole threw the threaded end, add a nice chain and wear it around my neck. It'll still look cool.