Eh, they're alright. You don't really gain anything by extending the shackles. (and keep in mind, 3" shackles will only lift your truck 1.5") Not really worth it, IMO.
Right now, I'm riding on BFG Mud Terrains, still open diffs front/rear, and have little trouble getting around whatever I have encountered. I've just never been a fan of shackle lifts.
The school on lifting that I preach, is to only go as high as you NEED to go, unless you need tons of suspension travel for something like rock crawling. Otherwise, stuff the biggest tires (and appropriate gearing to match) under the truck to gain ground clearance, but keep the roof as low as you can.
High center of gravity FTL.