I've got a set running on a completely standard 2-litre which, in my opinion, makes it go, rev and sound better than it would on a normal twin-choke - it's arguably better on fuel too, and idles etc equally as well. I'm not sure what the set-up would have cost, but I reckon it makes for a pretty decent, cheapish mod.
However, that's on a standard 100bhp or so engine, and let's just say I wont be ditching the 48s on my Ashton Pinto in favour of them.