I believe the Detroit locker and similar products are essentially limited slip diffs. They work well in some situations though are not normally very rugged, and are not comparable to a locked rear when it comes to hardcore offroading.
Though I have not looked into it very much, I understand that welded diffs are used for specialised applications (offroading and drift cars come to mind) but also get by on the trail and street though I can't imagine how and I'm sure its gonna be pretty bad on a lot of counts! ! !