Well, the Orbi wasn't a true mesh to begin with as the satellites always tried to connect to the base station. Its reflected in the initial review by SNB as well. They've recently upgraded firmware to allow multi-hop, but I think priority is still given to connection directly to the base station. Of course, if placement restrictions are not a problem I guess, optimal placement can be taken advantage of to benefit from this.
In my case due to the placement, the top floor satellite still always connects to the base station which I've tested while turning off one of the satellites while cleaning. The blinking on the satellite at times I assume, is when it checks which of the connections is stronger and connects to the better one. Apart from that, my internet tops out at 150 Mbps and usage on the top floor is mostly restricted to browsing, music or full HD streaming, while file transfers and 4K streaming mostly happen on the floor below. So real world usage is barely hampered.
In the OP's case though, a 2-pack should be enough which would provide the max throughput.
That cheap! Where? I can only find the 2 pack (dual band) one on Amazon.in at ~29K. The tri band is nowhere to be found. While on Amazon.com both are available much cheaper