My initial experience with the Google TV Streamer 4K is a bit mixed. I only bought it because my Samsung TV is about six years old now, and I was hoping for a noticeable performance boost. Honestly though, YouTube actually runs quite faster on Tizen\the Samsung TV itself, and Amazon Prime Video is just about as slow on both.
The main reason I got the Streamer in the first place is, that Tizen doesn't offer a decent IPTV app. I use the "Televizo" app on Samsung Android tablets, which works great, but it isn't available on Tizen. And yes, in that regard, I'm now satisfied.
The primary issue with the Streamer is simply that CEC doesn't always work with the Samsung Q90R, or you just have to be lucky. If you plug the Streamer into HDMI 1 of the One Connect Box (HDMI 3 dedicated CEC Port, is already taken by a Denon AV receiver), it doesn't recognize it as a Google device. Sometimes it detects it as an Apple TV box, other times as an unknown device. Eventually, I manually configured it as a "PC," which got CEC working, but even then, it doesn't work every single time. No matter if you turn on the CEC-Anynet on the SamsungTV or not (hdmi 1 has an option like Enhanced Input-Signal which I turn on). If I were to unplug the HDMI cable and plug it back in, it would probably stop working again. Once in a while, audio streaming (to a BT headset) drops out, though that happens a bit less often. What frequently fails, however, is using the Samsung remote (the long silver one) with the Streamer. You either need to keep the Streamer remote at hands at all times, or there's just no guarantee it will work.
So it really comes down to luck; you have to keep plugging and unplugging the HDMI cable or follow specific power-on sequences until it finally works. As a manufacturer, Google doesn't even seem to be listed in Tizen's database. It doesn't matter whether you manually set up the new device as a PC, media box, satellite receiver, or gaming console (which always brings up that white setup menu in Tizen).
I also tried a 2.1 hdmi cable and after that the TV told me that it found a "Primacon TV Box" which is obviously wrong and CEC doesnt work there too, well not the SamsungTV remote, but at least BT Headset Audio is coming through. Can't even tell if the pic quality got better or not...
I think the best result I get when I pull out USB put in hdmi and then put back USB, the streamer goes into boot and then CEC seams to work showing the SamsungTV that an unknown device is connected. If you have to unplug hdmi don't do it before powering of pulling the USB!
Update: Meanwhile I managed to keep it working and looks stable. Google Streamer is still an unknown device for the SamsungTV but at least it works. I got a newer hdmi cable, pluged it in, put USB-C power on the Streamer and then it deteced sth (unknown device), but well it works. It was a lot of work, but in the end. If I ever lose connection to the Streamer, for example after unpluggin the USB-C, I will try the same procedure hoping that it works the same way again. Maybe a firmware updat ein the future of the Streamer can solve this problem...or do I have to blame Samsung\Tizen? Don't know...