@aibtp 

Welcome to the community.

Compatibility: Yes, this is supported.
All Deco models, including different hardware versions, are compatible with each other and can work together to form a single seamless mesh network. In fact, TP-Link generally recommends using the most powerful Deco model as the main unit, so placing the XE75 units as the primary nodes is exactly the right approach.

Regarding advertised performance in a mixed setup:
While the units will work together, there are a few important things to keep in mind:

• Each Deco unit will operate according to its own hardware capabilities. The XE75 units (Wi-Fi 6E) will perform as high-performance nodes, while the M9 Plus units will be limited to their own Wi-Fi 5 specifications.
• In a mixed mesh network, the overall backhaul speed between units can be influenced by the capabilities of the connected nodes. Satellites communicate with the main unit, and the M9 Plus units will use their own radio specs for that backhaul link, which may not match the XE75's full potential.
• Wireless throughput and stability don't always scale linearly as more units are added — actual performance depends on house layout, distances between units, and obstacles.

In short, the XE75 units should perform strongly as the backbone of your network, but the M9 Plus satellites will be constrained by their own hardware. If maximizing performance across all nodes is a priority, using a full XE75 system would yield better overall results. That said, adding the M9 Plus units as satellites is a perfectly valid way to extend coverage in areas where top-tier speeds are less critical.

Thanks