Perhaps it won't knock down the big number on the dyno that the twin screw based units will, but it's still quite a capable system none the less. Whether it'll top them or not in peak horsepower is really irrelevant to anyone who isn't planning on tearing into their engine and fortifying the bottom end, since it's perfectly capable of making enough power to break the rods and pistons as it sits.
Look at even the latest 427R MM&FF tested that knocked down 12.4's through an automatic transmission in bone stock trim and went 12.2's on drag radials. A slightly looser converter, some computer and some shift schedule tuning and you've to yourself a high-11 second performer without cracking the nut on the supercharger pulley. Not too bad IMO.
I'm not saying the Roushcharger is the best of the bunch, but It's certainly not to be discounted simply because it's not built with a Twin Screw as it's base motivation.