I've got a Ruff Stuff one on my rear axle and a home-built guard that goes over the stock cover on my front axle.
Ruff Stuff do really good products and Dan the owner is really good at answering questions and getting parts out quickly.
save yer money and learn where yer diffs are. ive never even dented one. front or rear.
X2
I would consider myself to be quite 'hardcore' including driving 3-4 miles of rocky dry river bed from time to time and still haven't felt the need for thicker covers. The front cover is quite thick as stock, not like a landrover pressed tin affair.
I've only had one or two big hits on the diffs and they came from driving quite silly rocks at Seven Sisters, often when a bit wet (stupid, but fun
). For the cost, diff armor represents good value in my mind - one bad slip or slide into a rock and you can knacker a grand's worth of axle components (locker, new gear set + rebuild cost) and not be able to drive the Jeep for the rest of the offroading trip.