I've never used Pro Comp shocks myself, but I know people who have had bad experiences with them not lasting very well. One particular problem I've heard of is that the front shocks are too wide at the base, so when cross axled the the shocks come into contact with the springs,or something, and get damaged.
There are other gas shocks on the market for series Land-Rovers like Monroe and DeCarbon. I've never tried those either. Standard shocks seem to last well.
I'm tempted to modify my SIII so that a set of Defender 90 shock absorbers can be fitted. This should give better axle articulation.