Bottom line - opinions vary but the Powertrax does seem a bit severe compared to a suregrip (but probably not an old style Detroit locker), and a few people have raised questions as to their durability. I think they are primarily used by the 4x4 crowd.
One of the Mopar mags did a build on one, but it was in a low power application on an 8 1/4 IIRC. I've heard a few people rubbish their quality, although some have used them without trouble.
Don't forget both the cone-type and now the superior
clutch type SG are available new now, so that might be a better bet.I ended up going with a used clutch SG.......