Hi Danny, the difference is, the one you linked to, model 85181, is the tactical model with a new design forend featuring an integrated heat shield. The other non-tactical model does not have the integrated heat shield. That is the only difference, other than that, they are the same.
Both models accept direct mounting of Shield RMSc-pattern micro dot sights.
Stay safe & have a great day!

The Mossberg 940 Pro Tactical SPX and the 940 Pro Thunder Ranch are both high-quality, gas-operated, semi-automatic 12-gauge shotguns, but they have some key differences. The SPX is a more tactical model with features like an integrated heat shield, M-LOK slots on the forend and barrel clamp, and a 6-round shotshell carrier. The Thunder Ranch model, designed with input from Clint Smith of Thunder Ranch, is also optic-ready and features a Patriot Brown Cerakote finish. Both are reliable and suitable for defensive purposes, but the SPX leans towards a more modern, feature-rich tactical design.
Here's a more detailed comparison:
Mossberg 940 Pro Tactical SPX:
Focus: Tactical and defensive applications.
Features:
Optic-ready receiver with Shield RMSc footprint and adapter plates for other optic mounts.
Integrated heat shield and M-LOK slots on the forend.
Barrel clamp with M-LOK slots.
Vang Comp 6-round shotshell carrier.
Oversized, ambidextrous safety.
One-piece magazine tube.
Fiber optic ghost ring sights.
Durable Cerakote finish.
Redesigned, enlarged loading port.
Elongated elevator.
Action: Gas-operated.
Pros: Highly adaptable to different accessories and optic mounting, rugged design, reliable performance.

Hi Danny and welcome. The Mossberg 940 Pro Tactical SPX and the 940 Pro Thunder Ranch are both 12-gauge semi-automatic shotguns with enhanced features for tactical applications. The SPX is a more general tactical model with a focus on versatility and customization, while the Thunder Ranch is specifically designed in collaboration with Clint Smith of Thunder Ranch, incorporating his preferences for a home defense and tactical shotgun.
Key Differences:
Choke:
The 940 Pro Tactical SPX comes with Mossberg's Accu-Choke system and a factory-modified choke. The Thunder Ranch features a fixed cylinder choke.
Optic Mounting:
Both models are optic-ready, but the Thunder Ranch features patent-pending receiver cuts designed for direct mounting of Shield RMSc-pattern micro dot sights. The SPX includes adapter plates for mounting other optic footprints like RMR, Docter, and Leupold.
Sights:
The SPX comes with a tritium front sight with interchangeable color tubes. The Thunder Ranch features a fiber optic front sight.
Cerakote Finish:
The Thunder Ranch features a Cerakote finish, while the SPX may have Cerakote on select models (Flat Dark Earth and OD Green) on barreled actions.
Forend:
The SPX features an innovative forend with an integrated heat shield, two QD cups, and three M-LOK mounting slots. The Thunder Ranch forend is not specifically described in the provided materials.
Cheers, stay safe and enjoy!