Lightly Used Radiata Designs Victrix MP5 lower with super safety. Comes with slip trip and buffer. Lightly used. They're new online for $450 plus tax/shipping. Yours for $350. 

From the website:

This MP5 lower ships fully assembled with the fire control group already installed. Its design centers on the FCG while combining a polymer outer housing with steel-reinforced internals for structural integrity. The result is a lower built to endure intensive use and the repeated heating and cooling of heavy firing. Accepts AR-15 Grips that do not have a beavertail. pictured B5 but now ships with FCD GSA grip.

• Firearms grade Polymer + steel reinforced
• Aluminum 7075 slip trip
• Polyurethane Buffer (With Full Size models)
• 3.5lb Nickel Boron (NiBo) trigger (single stage)
• Ambi Selector
• Forward control Design GSA grip A1

https://nocturnalapparel.co/products/radiata-design-victrix

Meet near I10 and Cortaro