The foils are particularly popular because of the fact they are good in Commander. Serious Commander players tend to enjoy foiling out their decks, and in the right deck, Energy Flux can shut entire tables down. It’s particularly popular in Zur the Enchanter decks, because Zur’s effect can tutor it to the field from your deck.
While many players consider it “jank,” Energy Flux has its purposes. If you happen to find any Antiquities copies or foil Mercadian Masques copies, they’re good to pickup for long-term value. Non-foil Masques copies sell for about a quarter, so they aren’t anything special. Revised, 4th edition, and 5th edition copies sell for pennies. If you just want to play the card, you’re best off picking those up. But the foil is pretty nice.