Bought a single HS 210 for a 3-way switch, read all the reviews about whether you need one or two, from what I gathered one should work. Wired properly, both the HS 210 & dummy switches work manually.The issue came with turning on through app and scheduling, 1-2 seconds after you turn on the app shows as off and fixture stays on, you can shut off manually or through the app. The second issue comes with scheduling, with the on command the fixture turns on as expected but shows off in app after 1-2 seconds, this essentially disables the app from turning the fixture off since it thinks the fixture is off it does not send the off command. The final issue came with tech support, tried to chat, that was nearly impossible, long delays between chat and they sent me links to reset which did not work,. I then called, had to call twice, I won't get into all the details but the phone support is disastrous, they spent 25 mins going trough standard line of questioning then they want to finish the rest of support via e-mail, they don't respond right away to e-mail waiting now for 18 hours nothing yet. Have other tp-link single pole switches and wi-fi devices that work without an issue, super disappointed in the 3-way switch. I've read other posts abpiut this but no real fixes, lots of maybes.