Judging from the wiki, it says that you can't be knocked down when the effect is in place, though I think you only get ~10% damage reduction (depending on the points you have) :what:
The reduction is more like 80%. You also gain the ability to load a skill right after they explode (opposed to being knocked back and laying on the ground for a while) which helps in multi-aggro situations. As kitae said, you also gain the ability to Final Hit. You won't lose charges on magic bolts, advanced magic, or AR (because you don't get knocked back).
Also, almost all exploding mobs can be killed with a single smash, which can get the room cleared pretty fast (only need to smash 2 before a chain reaction goes off and finishes everything else). Unless you spawn multiple orbs at the same time, you can just use Windmill and clear the entire room instantly. Assuming you have a decent (~250+) amount of HP and maybe mana shield.
So, whether you want to tank them or not, it's still a very good thing to have.