The Pro deal is one of those "sign up now, cancel later" deals...so long as you have a GMail/Google Account (and who doesn't?). The Pro version gives you free access to ~8 games.
I've given it a quick go on my laptop this morning, on purposely not running the eGPU, so on embedded graphics and running to a 3440 x 1440 display, and (probably most pertinent) on WiFi. I was actually pretty impressed...I know a lot of places have slated the latency, compression artifacts etc, however the actual journey is fairly clean, and to my more casual eye I couldn't feel much in the way of sluggish controls. The game I tried (Grid, "serious" driving game) had fast moving graphics, so any compression visuals would be somewhat obscured.
None of my mobile devices support playback, and unless you have the Stadia Pro controller playing on a TV is a sort of no-go right now, which is a bit of a shame as the games available are more console/couch type things. Looking through what I have lying around, I should be able to get the Playstation controllers linked up to my laptop, and then I could plug the laptop into my Gaming TV and see how that works.
Here's a quick capture of me launching a game from browser (no sound as I forgot to enable it in OBS when I was capturing). One interesting point...recording is normally a performance hit on a game, however in this case it doesn't matter, as all the heavy lifting is done off-site. Apart from unskippable cut-scenes (and my atrocious driving...I'm blaming key controls) it's all quite slick. The video is not ultrawide, as OBS didn't like doing that.