On the other hand, a single metalworker can easily pay the upkeep of most ot the artifacts in play, so having a way to kill him could be a good idea if you want to run the flux.
And Metalworker is played in what deck exactly?
Anyway, you generally cannot put Energy Flux out unless your opponent has a decent number of artifacts on the table. For example, if you're playing against Stax, you would never go turn 1 Energy Flux off Lotus. The Stax player will simply chill for a bit and play a Joblin Welder or two, and play around the Flux, saving Moxes to be Welded in and out of play. If you opponent has one mox on the table, you wouldn't play Energy Flux. What you need to do is wait until there is a significant amount on the table (and therefore out of your opponent's deck) before you can play it. Change that situation I just mentioned: Stax goes first and plays 2 moxes, Joblin Welder, and City of Brass. You have Lotus and Energy Flux in hand. Here, it makes sense to bust out the Flux because your opponent's hand is decently drained and there are no artifacts in his graveyard. He will need to draw some artifact mana and find a way to get that Trinisphere/Crucible/Tangle Wire into his graveyard, since he can't play artifact mana and then have it for the next turn.
That's what you're trying to do. The thing to remember is that Joblin Welder is the best creature in the game right now, and he has plans that can foil your Energy Flux (remember it only triggers for artifacts in play at the beginning of the upkeep), and that Moxes can be used to pay the upkeep for other stuff before letting them go.
Hurkyl's Recall on your opponent's end step can be pretty devestating. Putting artifacts into the place where they cannot be Welded back is pretty solid. That, however, only buys you a turn, so you need to have something pretty amazing to follow it up. It's not too good if you follow that Recall with draw, land, go. That doesn't accomplish much at all. If you followed that play with Windfall, Wheel, or Timetwiser, that would be amazing.