Greater (or perfect) Bonding Runestones can be a great replacement for a Augment pet. Right now I am testing 3 Greater Bonding Runestones VS my Ioun Stone of might.
My Ioun stone of might has the following items:
- 3x Greater Bonding Runestone.
- 2x [Personalized Archmage's Ring +6] with [Azure Enchantment, Rank 8] and [Radiant Enchantment, Rank 8].
- 1x [Girdle of the Striker] with [Azure Enchantment, Rank 8] and [Radiant Enchantment, Rank 8].
Which results in the following stats being transferred to me:
2906 power
652 critical strike
939 armor penetration
2590 defense
My Zhentarium Warlock has the following items:
- 3x Greater Bonding Runestone.
- 2x [Talisman of the Loyal Commander] with [Azure Enchantment, Rank 8] and [Radiant Enchantment, Rank 8].
- 1x [Personalized Archmage's Ring +6] with [Azure Enchantment, Rank 8] and [Radiant Enchantment, Rank 8].
Which results in the following stats being transferredto me on 3 stacks:
5656 power
697 critical strike
1075 armor penetration
1956 recovery
1943 defense
Comparison

As you can see, I am getting (in some cases) far more stats with 3 stacks of Bonding Runestone than I get with my Ioun.
Power stat increased by 49%
Critial strike stat increased by 7%
Armor penetration stat increased by 13%
Recovery stat increased (added) by 100%
Defense stat decreased by 25%
Down sides
- Waiting time - It takes a couple seconds for my Warlock to apply all 3 stacks.
- Cooldown - The cooldown is 20 seconds.
- Loosing your companion - The companion can die or you can loose it, sometimes you need to resummon it.
My conclusion
All in all I think that the stat increase speaks for itself. It is a very good alternative, in my opinion probably even better than a Augment Companion if you have Perfect Bonding Runestunes, but it definitely works at Greater already. The downsides take some getting used to, but for me personally they are not a deal breaker.
Added (2016-05-04, 12:22 PM)
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WARNING
Bonding Runestones will be nerfed somewhere in the near future. Rumor has it that only 1 bonding will work, instead of all 3. So it might stop being better than a augment when that happens.