@Chicago_SH 

Would I still be able to install the HS210 if my circuit looks like the one below with the Load and Line in the same box #1?

  @ScottMan Any chance that you can provide a bit more detail or diagram on how to connect the satellite in the 4-way switch position, with assumption that the other main/satellite are wired as normal 3 way? I currently have working as a 3-way, with the 4-way disconnected (ie wires connected together to just pass through), but that is the most critical switch in the system and would LOVE to get this to work correctly. Your post is the first time i have seen anyone get it to work correctly. Much appreciated. 

@JHTOR as fate woud have it, I was just installing another set of 3-ways today and had TP Link's wiring diagram pulled up on my computer - so I modified it for this configuration.  The main thing you have to be sure to get right is being consistent on your traveler #1 and #2 wires.  Traveler #2 (black below) carries the load and needs to be tied to the Traveler #2 screw on all three switches. On the "4-way," you should have two wires tied to each screw.  Hope this helps!

FYI to all Seems like TP-Link is finally releasing (under the Tapo family of products) a 4-way compatible option. Seems to be a 3 way dimmer kit (S515D KIT), and another non-dimmer switch that may be compatible (S515). Have not yet purchased as don't seem to be shipping yet but if anyone has any luck getting these up and running, would be good to know!

https://community.tp-link.com/en/smart-home/forum/topic/720504