It's all over the web. http://www.groovypost.com/howto/stream-mirror-android-roku/ mirrors my experience that I find myself only able to cast to a ChromeCast on some things.
Seems we are beta testing a lot today.
Bob
Hi,
I have moto g first gen phone with me. After the android 5.0 update I am able to see the cast screen option. However when I go to cast screen option it doesn't detect my Samsung TV.
Has anyone faced the same issue. I have tried this with Samsung mobile phone (Samsung Note 2) and it has worked fine.

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic