I noticed that this works if I am on a FireTV Tablet ... but Does not Work on Android Tablets or Phones.
On FireTV when I select an Item on the Guide I get a ”Play To” suggestion and get a list of devices ... This does not work on Android Samsung Tablets or Galaxy Phones.
Play To hasn't been working for more than a year on my Samsung phone. But I never really wanted to use it, so I ignored it. Although at one time it would list every device on my network, just like Youtube currently does.
It really helps in my household because I have a family member that has a problem using these small remotes, so they use the Fire tablet to search and use Play To... at least for now I am glad the Fire Tablets work. It is so much easier to bring up Channels DVR on a tablet search for a movie hit play to and it is good to go.. I started testing it yesterday and it woke up my FireTV and Started playing the movie it also switched HDMI ports. 
Took this feature for granted but I love it now.
I like using the Fire TV remotes, they are nearly perfect for me. Except when I need to enter text strings such as passwords/user names/ip adresses, then I like to use my phones FireTV app.