hi ,I have a Calmini LSD in the front axle and I m very happy with it.
2 main reasons
1.In mud terrain ,I saw that when the rear locker starts digging deep in the mud,the front LSD is the one that pulls the truck out of the mudhole
2.Again when driving with 4wd,the front LSD operates very well even when turning,and applies the best possible torqe to the front wheels,elliminating slippage.
I didnt used a locker in the front cause I want to protect the sensitive front halfshafts.The axle housing breakage was solved with the Anvil and a steel 3rd member.But the halfshafts remain a problem to be solved.And ,with a locker ,I believe I would have to stock at least 4 pieces ,just to be sure...

The LSD is strong enough (together with a rear locker) to help the truck overcome difficult and especially muddy obstacles.
On the other hand if I knew that I would have to drive everytime on rocky terrain,in that case I would have installed a locker in the front.
What you ll use ,also depends on the type of terrain most of the time you have to deal with.I believe for 80% rocks-20 % mud lockers all around is the best.
For 80% mud and 20 %rocks ,a rear locker and a front LSD is the best.
Hope this helps.