The Deco 9 should be compatible and expandable with any Deco product. This means that a single unit of a Deco product can also be purchased and integrated.

The Deco systems can be expanded with any other model, i.e. it may make sense to combine a set of 2 Deco M4s or even E4s with the system and thus perhaps achieve even better coverage with more units. A single P9 should cost about the same as a set of 2 M4s or 3 E4s. Some of the individual devices cost almost more than a set of 2.

A restart of the main router will probably help. Otherwise, the P9 can be reset and reconfigured.

I also experienced the same but for only 1 unit. It goes offline and can't connect with the power line or wifi, this happens randomly .

Unfortunately, there is no manual. I only found these two links with FAQ's: https://www.tp-link.com/ch/support/faq/2401/ https://www.tp-link.com/ch/support/faq/1464/

Yes, it is compatible. Each P9 router has two 1 Gbit/s ports.

It’s a 2 pin plug so works with both

Hello Cwalwal, Yep, all three can be connected with an Ethernet cable. Can only recommend the product! Greetings

Well, I've already noticed that it's never worth buying a set of 2. You can get a set of 3 for a little more, or vice versa, you can even get a set of 3 for less (like the Deco M5). However, I don't think that the prices for a set of 2 would be lowered because of that. Therefore, I would always go for the 3-piece set, because you get more for almost the same or less and you can quickly expand at home if necessary because you already have a third device and if two are enough, you already have a spare part at home if something should break :).