After years and years of shilling for this device on these forums, I finally took a plunge late last year and bought the NVidia Shield TV Pro model.
I only started using it for a few days and my experience is limited so far, but I will share some of the older streamers and experience with Shield in comparison.
My very first HTPC was a mini-ITX DIY Atom 330/ION-based box encased in a fairly small box. Based on the Zotac 1st ION platform. I think I used openElec/Kodi Back then.
Then it was replaced for Asus Atom eePC/ION2 tiny-SFF pc also running OpenElec - slightly faster, but no major improvement. That box ran for quite a long time.
Then came the turn of several MediaTek-based s905x boxes, like Khadas VIM, running OpenElec's fork - LibreElec - these offered very low power. Native H265 decode and HD Audio pass-thru to AVR. Right about this time I switched from getting all of my media managed by Kodi to A Plex server and since that point using exclusively Plex Client on LibreElec/Kodi only as a basic platform.
After few years s905x devs mostly let it stagnate, moving to newer platforms. Around that time I switched to Amazon FireTV 4k dongle and it worked mostly ok for a few years. Having minor issues plus upgraditis kicked in and I splurged on Sheild Pro 2019 model.
Performance: GUI feels much more fluent, responsive than basically any other box I used before, on par with Apple TV 2/3 boxes.
Video decoding - so far everything works. I Will report if I find outliers.
Sound - passthrough seems to be working - it even detected and suggested passthrough all by itself.
Upscaling - this is absolutely unique to Shield and it can perform AI upscaling - it doesn't work on all resolution sources - I wasn't yet able to find a proper 480p source to upscale (cropped resolutions aren't supported), but it does a stellar job upscaling 720p to 1080p.
Remote: BT remote works well. I am getting used to it, feels comfortable to hold, but rewind buttons locations will take getting used to.
Cons: Not much at this point. I guess voice recognition is surprisingly even worse than Alexa's on FireTV. Netflix dedicated button is a minor annoyance as I don't use Netflix, Luckily there is a way to reprogram that button to Plex, I just haven't tried it yet.