IMO, I would use the spool if mainly for a trail rig. However, if 50% or more is daily drivin', go with the lock-right.
My experience:
87 sami. 4:1, stock r&p, 30x11.5x15 TSL/SX.
I ran a lock-right in the rear for 2+ years. I broke 2 sets of stock sidegears! And the lockright was somewhat hard on my axle splines.
So I put in a minispool & new axle shafts. Now it is very tight and GREAT offroad (no lock-right slop!). However, I still daily drive it 30%+ on the pavement. This is a pain in the rear (no pun intended). It's VERY noisy on the road, and so squeely in parking lots. Feels like things are binding up bad (depending on tire pressure) on cornering. If running my summer BFG A/T's, it hops, jumps, kicks as you go around corners - so annoying. I will be going back to the lock-right ASAP to get the slop back in in the rear - I miss it.
ps - I've had a lock-right in the front for 3+ and love it.