I welded the diff in my 240sx. This was by far the best modification I have made to the car for any money and the best part is that it was free and easy. I willl admit to having no experience with a proper LSD unit but lots with an open diff. Buying something for $800US was not an option for me.

Once you weld it you can not change your mind though. So have a spare around if you want to experiment.