It's not hard to keep up, it's just a pain in the ass as a mandatory raiding talent. You either hit it to early and nothing happens or you hit it too late but in that .5s-1s window you refreshed a dot without 15% haste, lowering its damage. And then your power auras stop working because it doesn't stack with Heroism and you think you just let it fall off and recast it for no effect...
Personally, I get really upset with myself when I refresh a dot without ISF up, and while I will eventually get over myself and just play better I would prefer to just not have to deal with a bullshit ability that requires dynamic haste timing.