Prometheus releases their classic hard piston, a technological benchmark for reinforced pistons. This version is specifically designed to drop in to the new Marui SOPMOD so the new kid on the block can now enjoy the glories of Prometheus as much as his older siblings.
Tokyo Marui, like all Japanese brands, are restricted by Japanese law to a weapon shooting energy of around 280 fps. What this means is that their weapons are low power with low power springs.
When these weapons get abroad, often the springs are upgraded but as the internals are designed for 280 fps then other parts need to be reinforced. In particular, pistons are high stress parts and will need to be replaced with stronger versions in higher power setups.
The Tokyo Marui SOPMOD M4 / Marui Scar-L is one of the newer Marui weapons. It features a lot of cutting edge features at the simple cost of being so new that there are not that many aftermarket parts for it yet. That said, that list of parts is still growing.