I have a question. Since it mentions "When a monster on the field activates its effect" & "the activating player", that means that your opponent can use it too? If yes, this is really a bad card.
If not, it may see some play in some Sartorius/Desperado decks. A 50% chance each turn of negate an effect is not that bad actually.
Not sure why you think Second Coin Toss only works on your own coin tosses. It gives no craps who's tossing the coin. (Heck, it even works on cards like The Paths of Destiny that require both to.)
I tried it though and it really doesn't work although you are right - it should work on any coin toss not just your own, but it doesn't work with head judging.