Yes, it's like a insta PLOX that does not need an Gardevior. Thing is, you have to put it onto your Bench to Activate it which might take up valuable Bench space. But, I guess you can always put some SSU in your deck and hope you flip right.
Also, since it only works for 1 turn, the slow down is minor. And, if they play like me, they can just charge up a Umbreon or Espeon with Multi and switch to keep Leafeon save from harm.