I know most of our guild at this point is not using a threat meter. Because of Hakkars mind control and the need for three tanks using one really helps. We dont want hakkar pulled into the group by a clothie after a aggro wipe. You can download it at:
http://www.curse-gaming.com/en/wow/addons-3488-1-klhthreatmeter.html



I find it also helps if most of us have an idea of what to expect from the fight here is a good link to review the strat:
http://www.wowwiki.com/Hakkar_the_Soulflayer

Get excited we are doing great