In many ways, depending on how well GX cards become in this Sun & Moon Meta, I say watch out for this card. It proves that Stage 1 and 2 GX's have one major exploitable vulnerability: They evolve from fairly low-HP Pre-evolutions. For instance, Solgaleo, Lunala, and Primarina -GX, etc. will often be played on top of 60 HP basics, usually bypassing the stage 1 with Rare Candy - so you can potentially just do the 60 damage upon them, and then use Espeon-EX's Miraculous Shine to finish the Knockout(s) with one single energy!
Of course, there is a drawback: You did not exactly knock out the GX card, so you only get one prize card for the normal basic you just devolved. But despite that, just forcing your opponent to re-evolve a Basic into a stage 2 can also be rewarding as well. I can see this card as a easy tech in the future.