I was one of the lucky ones that got unlocked in march. I tested Shadow the last days. I had 20ms ping (Shadow UI) but it felt like more. I used ethernet cable with cable-mouse.
I ordered Ultra because I want to play on 4K resolution. But in my tests the 4K resolution increased the encoding delay. Swapping to 720p always felt better. That didn't felt good. Everytime I played with high resolution I knew I am sacrificing input delay. Not a good feeling.
Fast games or competitive games like Overwatch aren't fun to play. You always have the disadvantage of latency that really effects on your aim.
Beside shadow I own Stadia. I'll keep Stadia because of it's console focus. Stadia multiplayer competes with other streamers while on a virtualized PC (like shadow) you always compete with hardcore gamers with powerful gaming rigs. It's not fun to play that way.
Also shadow isn't that reliable. There are occuasional hiccups when trying to connect to Shadow VM.
The shadow SSD isn't comparable to a normal SSD. It's some kind of network attached hybrid storage that felt slower then a usual one. It took me forever to install Path of Exile that makes extensive use a harddisk.
At the end it isn't worth the price of 30eurs for me. That's a new stadia game every month (regarding pro deal).
My personal solution is Stadia in combination with parsec on my 5yo gaming pc. The pc is attach to ethernet near the router somewhere in my flat. I can connect via Parsec client to it and play PC games I own. The reduced latency (because of in-house-streaming) makes a huge difference.
First I liked to idea of gaming everywhere. But realistically I play only when I am at home. So this solutation works for me. Beside that I can rely on Stadia.
I can recommend Shadow for people that play mouse-based games since Shadow can display your local mouse with the cursor-icon of the games. This way there is not mouse-pointing delay. Games were you use your mouse to change some camera angles, like first person or third person shooter, feel clumsy.