@ScottMan 

In you video, you had mentioned that if you install the smartswitch at the load side, the smart switch may lose power for a split second if one of the dumb sritched was flipped to slow.  My setup is where the line comes in, there is not a neutral wire there and i cant pull one.  However at the load side, there is a neutral wire available along with another line.  What would happen if i used another line wire to power the smart switch at the load side? Would this work and would this be an electrical hazard?  

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

@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!

  @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. 

  @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?

  @septer012 

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?

I have a 4 way setup and switched the two 3 ways to smart switches and they work fine and as expected. However I really wish I could use smart dimmers instead of just on / off switches. 

Wish there was a way beyond buying 2 kits. 

  @board4mic Thank you! I was afraid that I would have to do a micky-mouse to make my 4 way work. Nice!

board4mic wrote

update.  i replaced both of the 3-way switches with TP smart switches and left the 4-way "dumb" switch in the circuit.  This set up is working perfectly for me.

  @Chicago_SH 

I installed two Kasa 3-way switches and left two manual 4-way switches for a 5-way configuration. I connected them to the Kasa app as paired 3-way switches.

The app does not always report the correct status of on or off. Also, if the switch is turned off at the first installed Kasa 3-way switch, none of the other switches can turn the lights on.

Any ideas?