Double-Edged Sword Mastery

Not everyone uses Double Edged Mastery. You just have to consider who you are using and if it benefits them. Here are some common examples :

-- Melee champions get a 2% damage boost for an intake of 1% extra damage. This effectively increases the damage they deal by 1%. So this is a net gain where a ranged unit is dealing more damage but receiving the same percentage increase back, so there isn't a huge gain there. Not saying that I would never use this on a ranged champ or to always use it on a melee champ, but I have seen this argument for why it is used.

-- If you are a burst assassin than this may be good for you. If all you want to do is 100 to 0 somebody, then this increases your damage output. It doesn't matter that you take more damage because the idea isn't to do a sustained fight, just kill the enemy as fast as possible and leave. This helps you do that.

--If you are going for a big brawler who will have lifesteal and health. This should allow you to effectively negate the bad portion of this mastery in a sustained battle. Having health is important here. If you don't have a big enough pool of health than you are liable to get bursted to death, this mastery makes you easier to burst.

--Also remember that most runes and masteries are geared towards your early game plan. If you plan to stay in lane and farm / trade when it happens, than you probably don't want this mastery as it has more of an impact early game than it does later game. Later game items make much more of an impact. However, if you plan to try and bully somebody out of lane by being ultra aggressive, than this mastery may suite you well. Take it according to playstyle and see how you like it.

Hope that helps a little

Depends, it's better in lane than teamfights because you take so much more damage than you deal, if you have that extra point i would get expose weakness, it stacks with your allies expose weakness, can be pretty strong.

I do if the champ has a form of sustain, but I generally avoid it for champs that can't heal or shield themselves as the extra damage you take adds up over time.

sometimes for melee bruisers... considering for another melees...

I'd only use it on melee for the 2% vs. 1%. I would never spend a mastery point for a 1.5% damage increase and take 1.5% more damage on a ranged champion. Probably better to pick up 1.25% attack speed or cooldown reduction. Besides, I consider feast almost mandatory for laners so I often need to take butcher for +2 npc damage.

I use it on Rumble although I probably shouldn't because I suck as Rumble lol

Don't use it on much else because I favor ranged champions.