I touched one of these today. All I can say is

The only bad things I could say are that they put your wrists at an awkward angle (think Dreamcast) and it's weighted poorly (very back heavy), and heavy overall. But besides that it's an absolutely incredible piece of hardware, it feels very well built. I tried some boring android game on it which was fine, but the best demo of it was playing Skyrim on it. There was no lag or lack of response from the controls, it felt quite natural. The other good part is that they were running the same game on a monitor behind it and you could see it was running in some low res low detail mode, because it was a blurry jaggy mess. It was probably running at 720p since that's what the Shield screen runs at, so you get a bit of a free performance boost from using lower detail modes.
Couldn't be more impressed with it, just wish it was sub $300 instead of $349. Have gone from mildly interested to trying to find ways to justify buying one to the gf now.