I've been using the original Kishi since it came out (think there's a new updated model now). It's solid enough, obviously not going to be as good to use as the official console controller but it gets the job done. Personally speaking it's not ideal that it obstructs my phone's headphone jack, but appreciate most phone manufacturers have already done this themselves anyway.
The biggest complaint is probably how 'squishy' all the buttons feel, especially the triggers which are pretty awful to be honest. However I mainly use xCloud for slower-paced indie stuff or the Yakuza games so it functions well enough - trying to play a Forza or something might be a different story.