This product was designed to create more space in the engine compartment. Combining two reservoirs into a single component frees up space for intercooler tube placement, easier maintenance, access to the engine, and durability.
"The OEM plastic reservoirs are replaced with CNC laser cut and formed aluminum that is hand TIG welded to provide reliability under the most severe conditions. CNC machined cap retainers assure these caps will never pop off. All fittings and hose are DOT approved, meaning they cost more, but are actually designed to provide reliability under extreme temperatures and chemical exposure. Designed to work with 2008-2016 WRX/STI models"