Confused about Combustion

[:1]Hi, I just reactivated my account and hadn't played since SC2 beta came out if I remember well. I have lots of toons, mostly played my mage since day 1 through pre-BC. I leveled it back with the other expansions but hadn't made him my main since.

I decided to keep my mage as my main character for Cata and focus on him again. I was still familiar with most of the stuff with my mage (still played him some) until that last huge patch.

I played mostly as Frost since I reactivated but am also checking fire out (haven't tested arcane yet). I must say that I'm pretty confused about the new confusion and don't quite understand what it does. It think I just read someone mentioning combustion used to AOE people in AV o_O.

From what I understand, the new combustion deals roughly 2k instant damage and removes all the fire DoTs you have on every target to move them onto that one target, stacking them in 1 big new fire DoT?? It's really unclear to me as to what it does and if it's even good at all. I've never been a big fan of DoTs but wouldn't this combustion be more or less ''horrible'' for organised PvP since it allows the enemy healer to basically dispell all of your fire DoTs at once in the new combustion form?
This is what happens when you use combustion.

1. Your target takes a little fire damage (not very important)
2. The total dps of all fire dots on your target is recorded.
3. A new dot, called combustion, is put on your target that ticks every second for that dps. Both the initial hit and all the dot ticks are capable of critting, and it is spreadable with impact for massive aoe damage.
4. All your fire dots are still on your target.
Ah ok thanks!

So it means it basically doubles the DoTs on that target? (and the best use obviously is with impact).
To extend on what Karrok alredy pointed out is that combustion ticks every 1 second (with no haste you will get 10 hits of it, which means 10 chances of a 3.8-4.5k optimal combustion crits in ICC 25 gear)

Since all your dots take longer that 1 sec to tick exept combustion, combustion becomes your most sensitive DoT to haste. Because of the rewamp to DoTs and haste mechanics and the interactions of the 2 it is easy to get 3 to 4 ticks extra whidout timing cooldowns, and more with the timing of possible haste cooldowns like trinket procs of herbalisam cooldown (not sure if heroisam/bloodlust stack with DoTs).

So this adds a extremly haste sensitive cooldown to your repertoar of spells where its easy to increase its efficiency by 30-40% while still gearing more towards crit.

On the new DoT mechanics you can read a shadow priest article on MMO-champion that dose a decent job at explaining it and can be applied to any DoTs/channel spells

http://www.mmo-champion.com/threads/712942-Guide-Channelled-Spell-amp-DoT-Mechanics-in-Cataclysm