my talent buildFollow

Depends on what you want to do.

If you want Conflagrate there's really no reason to get Shadow Mastery. The build you linked is a common PvP build focusing on burst damage.

If you go Affliction, at least get Dark Pact. Otherwise you'll still just burn through your mana in less than a minute.

Personally I would pick the build you linked for PvP. For PvE I'd go Dark Pact/Ruin.

Every time it hits, I think. Every Hellfire/Rain of Fire tick or on Soul Fire impact.

Not worth getting though. In my humble opinion. You won't be using Soul Fire and Hellfire THAT much. Unless you plan on AOE grinding with someone who can heal you.

The reason why the talent sucks is that it isn't a stun that procs, it's a daze effect. The daze pretty much just slows the target down for a brief amount of time. There are much better choices for talents than pyroclasm.