This card is not better then Hidden Guerillas. Hidden Guerillas is much better then this, it serves a similar mental effect that Mystic Remoria does. While its in play, it makes your opponent think twice about playing an artifact and by doing so creates tempo. All the trap card does is catch your opponent off guard. Also, if you are running green, your most likely going to run Tarmogoyf, and having enchantment that can go into your graveyard is much better then just another instant card.
The problem, though, is that they will take whichever path is more sensible at the time. For example, with Remora, normally the best path is to sacrifice your tempo and wait it out. With Guerillas, it can really depend a lot more on the game state, making the card worse. If they are at 20 and can see a path to winning, they will play out their mana and ignore it; if not, they will simply wait. In either case, they get to decide if it looks more like a Chalice at 0 or a creature. With this card, there is no option, and it is always a creature.
If you are gaining tempo off Hidden Guerillas, that means that they must be afraid of it (and assuming your opponent isn't a bad player). In that situation, it would just be better to have a creature.
I think the only advantages that this has over Tarmogoyf are the fact that it will generally have a higher starting power on the first few turns, and that it can sometimes be played as an instant blocker. However, I would agree that Tarmogoyf is generally the safer choice.