These benchmarks measure up and downlink, 2.4 and 5 GHz throughput at each system node, by "walking" the octoScope Pal dual-band test client from node to node. Since tests are made with 0 dB attenuation between the Pal test client and each system node, all measurements are best case. The purpose of this test is to measure the best case throughput available on each band at each mesh node. Once you get beyond the root node, this test shows how backhaul performance affects the ability of a node to deliver throughput.
In the following charts, A bars represent the root node, B bars the Hop 1 node and C bars the Hop 2 node for the Deco M5 only. The C bars for NETGEAR Orbi and Deco M9+ show throughput measured at the Hop 1 node with 21 dB of attenuation applied between the node and octoScope Pal STA. The attenuation is meant to simulate the additional OTA (Over The Air) signal loss from moving the STA away from the mesh node. This is our standard for this test for two-node systems.
2.4 GHz downlink results show the advantage of the separate 5 GHz backhaul link used by the Orbi and M9+. Both turn in significantly higher throughput for the B and C bars, while the M5's throughput drops for both.
Wi-Fi System Performance - 2.4 GHz downlink
2.4 GHz uplink shows the same steep Deco M5 decline for the B and C cases. We can also see the affect of lower uplink backhaul bandwidth in the M9+'s throughput dropoff between B and C.
Wi-Fi System Performance - 2.4 GHz uplink
Orbi and the M9+ track closely for cases B and C for the 5 GHz downlink benchmark.
Wi-Fi System Performance - 5 GHz downlink
5 GHz uplink again shows Orbi and the M9+ tracking closely for case B. But the M9+ really falls down when 21 dB of attenuation is added between the mesh node and octoScope Pal STA.
Wi-Fi System Performance - 5 GHz uplink
Our Wi-Fi System capacity test uses three 2x2 AC clients; a 2.4 GHz client is connected to the root node and 5 GHz to the others. For Test Cases A and B, 0 dB was applied between the Pals and mesh nodes. For Test Case C, 0 dB was applied between the Pal and Hop 2 mesh node for the three-node Deco M5. For the two node Orbi and Deco M9+, 21 dB of attenuation was applied between the Pal and Hop 1 mesh node.
This test runs for 30 minutes to see if any attempts are made to balance throughput by throttling backhaul or client bandwidth so that more bandwidth is made available to the other. It also serves as a sort of stress test to see how the mesh stands up under load.
I had a difficult time getting through the full 30 minute test for the M9+. For some reason, after a few minutes, the clients would still be connected, but the TCP/IP connection would die for one or more Pals. I ran this test at least a half dozen times and, in the end, had to put together the test results shown below from separate downlink and uplink test runs.
The Capacity bar charts show throughput for the three test clients in each direction. One of the dirty little secrets of mesh Wi-Fi systems that don't have a separate radio for backhaul is that loading the root node usually starves leaf nodes for bandwidth. It doesn't have to be this way; the system could balance the root node radio to limit device bandwidth to provide more bandwidth to backhaul. I've yet to see this happen, however.
The downlink results show the Deco M5 second hop (Test Case C) delivering very little bandwidth due to radios doing double duty for fronthaul (client connect) and backhaul (mesh node connect). Both Orbi and the Deco M9 Plus do better for Test Cases B and C, but the TP-Link outdoes Orbi in both cases.
Wi-Fi System Capacity - down
Uplink shows similar results, but with the M9+ again the best out of the three products compared.
Wi-Fi System Capacity - up
Looking at a time plots of results provides additional insight. The downlink plot shows high throughput variation for all three STAs. This does not look like a system that behaves well under load!
Wi-Fi System Capacity vs. time - Downlink
Uplink looks a bit better and more like I would expect, with Traffic Pair 3 yielding lower throughput due to lower signal level from the 21 dB of inserted attenuation.
Wi-Fi System Capacity vs. time - Uplink
With a rank of #5 out of 15 Wi-Fi systems tested, the Deco M9 Plus lands right at the bottom of the top third of products. The good news is that its subranks are good for benchmarks that count, i.e. system, capacity and 5 GHz RvR. And it outranks—by a lot—products like Linksys' dual-band Velop (#13) and ASUS Lyra (#14) and Lyra Trio (#12). But I'm not comfortable with the product's ability to hold up under heavy load, given the difficulty I had getting a complete run on our Capacity tests.
Ranker Performance Summary
The ascending price sort of the Ranker can be used to find products with the best price/performance and it shows the NETGEAR Orbi RBK40 ranked #4 and $60 cheaper at $240. At $300 for two nodes, the M9 Plus is competing with the #1 ranked original RBK50 Orbi (~$330) and two node version of Linksys Tri-band Velop ($300) ranked #2.
In the end, the TP-Link Deco M9 Plus delivers more value than most other Wi-Fi systems with its smart home Bluetooth/Wi-Fi/Zigbee hub and automation, IFTTT and Alexa compatibility, web content filtering and all-device antivirus features bundled in at no additional cost. The question is whether buyers value those features enough to accept somewhat lower performance than competing products, priced the same or lower, without all those features.