There's been a few threads about them on the AirgunBBS
I've tried a couple at Donny Airgun Range (The customer's couldn't get them to group no matter what pellet they put through them, so asked if I'd try).
Out of the 2 I've personally tried, I couldn't get a group better than 1" at 30 yards.
That's not an exhaustive test, and may also be more to do with the rifle than the barrel - but it's what I found with the two I've tried. There was a 3rd one as well, which I didn't try, but the customer reported the same thing - terrible groups.
To add balance to that observation, there are a few people on the AirgunBBS who say that their ST barrels put in groups that are as good as the groups they get from their other guns.
The general feeling is also that the barrels need a cleaning regime to get the best from them (just like other barrels really).
So.. it might be that the one's I've tried just had some issues and isn't indicative of all ST barrels.
However..... If the people who have found them to group well have only found them at best to group as well as other barrels whilst still requiring a regular cleaning regime, you've got to ask yourself the question - "What benefit are they over other tried and tested barrels?"
I've not heard a single report where someone has said (let alone demonstrated) that their ST barrel gives any sort of advantage over a fairly bog standard LW barrel.
Are they supposed to be better than what we've already got?