its exerting constant pressure against the side gears, and that will help create a limited slip effect, but can't positively 'lock' anything together. Its totally dependant on the side gears gripping the carrier, there's no mechanical locking device in the unit.

I didn't mean to insult with the 'low power' remark. In the grand scheme of things, a high powered 1400cc engine is still a relatively low power car.
That Swift was a rocketship even when it was naturally aspirated, and spun to over 9000rpm. The PG worked well for him until he turboed it, with over 240bhp. All of a sudden the PG had absolutely no effect. If it had a method of mechanically locking the centre, it would still have worked - it might have broken, but it would have worked...

I'm not saying they're sh*!, they do work in low power applications, but they aren't a locker.