I like how they work now. They shouldn't be too effective as mines, just as the Rook can't build 6 permanent towers. A little extra defense quickly becomes way too much defense.The use of the ability is twofold right now, you can both use them as grenades, and as "stop the enemy in the future". I like skills that have a hybrid function. Gives more range (in the philosophical sense) to the character.
I think it's a good aoe skill, and every assassin willl need it against generals.
I don't like that you throw 1-2-3 at a time, and that 2-3 explode instantly however. Sometimes I get the feeling that they go off on the same mob. It feels like a waste. Either give the extras timers, or spread them out just a bit more to prevent the rather large overlap.
Poor scaling affects all AOE skills except swipe attacks. I don't like that either, but I guess I see the point (general's minions would die like flies otherwise, their health is static I think).