It's easy to tell if your FX Impact has a Power Block on it or not:

FX Impact M3 Power Block

The upgraded Power Block FX Impact was released officially in April, but unofficially, starting in January, unbranded Power Blocks were an in-line change to the rifle.

That means your newly purchased FX Impact might have a Power Block on it already, even if it doesn’t have the laser engraving saying “Power Block”.

The easiest way to tell is to remove the magazine, and count how many recessed holes are on the back of the block. The old block has 6 recessed holes, the Power Block only has 4.

The other difference is that the back of the new Power Block Valvetube (silver circle on the back base of the block) has a beveled edge whereas the old block Valvetube has a clean flush edge.

Hope this clears up confusion as depending on where you live in the world, there might still be unbranded Power-Blocks being offered for sale.