Hey everyone
Update time. So after 3 days of what seemed great stability, first problem. Family member complained of no internet on their PC which I thought "meh it happens" as 2 hours later when I got in I checked the PC and all was fine. Logs showed nothing that I could see. I should have maybe suspected a problem since the PPPoE link showed close to 4 days uptime still.
About half an hour ago I noticed the printer was offline. The first sign of an actual problem. I know that connects to a satellite (192.168.2.1) so I try to ping the satellite from a wired client on main node (192.168.1.1). Could not reach it at all. I then switch on the problem PC (as stated above) also auto connected to that node and sure enough no internet. I could ping locally to 192.168.2.1 and see the printer online since it was connected to the same node but reaching 192.168.1.1 was not happening.
192.168.1.1 luci web interface showed the mesh point was still associated so I don't know what happened. To fix it I just did a reboot of 192.168.2.1 and all of a sudden everything worked again. I was going to try and get some logs or something but since the problem pc didn't have putty (and no internet access to download putty) I was kind of stuck.
I don't know if I should blame my setup skills for this but then again it did work for what appeared 3 days so I can't have been miles off. I will say that the other satellite node (192.168.3.1) has not shown a problem that I know of anyway. While this was going on I could ping that from 192.168.1.1 just fine and access luci etc.
I'm not one for conspiracy and it literally makes no sense but I think it might be a hardware problem. People with the stock oem firmware of the Zyxel Multy M1 (WSM20) said they also have problems with reliability (one reason I wondered why it's so cheap). One person even joked that it's called Multy because you have to make multiple trips to a customers home to get it working again.
I thought that should just be something that OpenWRT fixed since it's different software but maybe it is actually hardware. I don't know how though so I'm probably just stupid. The thing is the family member works from home so having reliable internet access is a must that I will have to go back to eero.
I might send the 3 WSM20 back. Don't get me wrong it's pretty insane when it does work. I was able to do a waveform bufferbloat test and get an A+ rating for a wireless client connected via a mesh node... let's see eero do that.
I only have approx 60 Mbps internet. I installed htop and saw spikes of 75% CPU when doing speedtest with sqm (even non sqm I saw 55% or so). There's no way that if I was to get faster internet that the router could handle sqm at say 150 Mbps plus mesh. I think it makes more sense to send them back and get something with a better CPU, plus it will completely make sure hardware isn't a problem for reliability. I don't see many people complain about the Netgear WAX206 for example. It is quite annoying that 1 WAX206 is just about the price of 3 WSM20. 
I guess I could look into the WDS thing but I'd need to reread how to do that. Can't be much different from mesh I guess. I don't really want to put the family member under more unneeded stress of not having internet though.