it depends on how well the welder doing it preps the surfaces and knows what he is doing and how to do it... the best way from what i have heard is to use a plate in the spiders.....
doing it improperly can lead to catastrophic failure
lots of people will say don't do it, it is unsafe, lots will say it is just fine.... safety is up to you... it will not perform like an open differential, and you can't go hotrodding it all the time, unless you accept that carnage may result